Issue:
Bug: Rename `s3` feature flag to `aws_s3`



Rename `s3` feature flag to `aws_s3`. This change is required so that current storage scheme becomes distinguishable, especially if in future new storage implementations like a AWS S3 alternative is integrated.

Pull request description:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
This PR renames s3 feature flag to aws_s3 so that current storage scheme is distinguishable, especially if in future new storage implementations like a AWS S3 alternative is integrated.

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!--
Provide links to the files with corresponding changes.

Following are the paths where you can find config files:
1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
-->


## Motivation and Context
<!--
Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

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## How did you test it?
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Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
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Just a rename of feature flag, so basic sanity testing should work

## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible
- [ ] I added a [CHANGELOG](/CHANGELOG.md) entry if applicable


Testing:

Just a rename of feature flag, so basic sanity testing should work

Patch:
diff --git a/crates/router/Cargo.toml b/crates/router/Cargo.toml
index 8897fdac2c2..88272033fb0 100644
--- a/crates/router/Cargo.toml
+++ b/crates/router/Cargo.toml
@@ -10,12 +10,12 @@ license.workspace = true
 
 [features]
 default = ["kv_store", "stripe", "oltp", "olap", "backwards_compatibility", "accounts_cache", "dummy_connector", "payouts", "business_profile_routing", "connector_choice_mca_id", "profile_specific_fallback_routing", "retry", "frm"]
-s3 = ["dep:aws-sdk-s3", "dep:aws-config"]
+aws_s3 = ["dep:aws-sdk-s3", "dep:aws-config"]
 kms = ["external_services/kms", "dep:aws-config"]
 email = ["external_services/email", "dep:aws-config", "olap"]
 frm = []
 stripe = ["dep:serde_qs"]
-release = ["kms", "stripe", "s3", "email", "backwards_compatibility", "business_profile_routing", "accounts_cache", "kv_store", "connector_choice_mca_id", "profile_specific_fallback_routing", "vergen", "recon"]
+release = ["kms", "stripe", "aws_s3", "email", "backwards_compatibility", "business_profile_routing", "accounts_cache", "kv_store", "connector_choice_mca_id", "profile_specific_fallback_routing", "vergen", "recon"]
 olap = ["data_models/olap", "storage_impl/olap", "scheduler/olap", "dep:analytics"]
 oltp = ["storage_impl/oltp"]
 kv_store = ["scheduler/kv_store"]
diff --git a/crates/router/src/configs/settings.rs b/crates/router/src/configs/settings.rs
index 3d93c2f188b..b674c503542 100644
--- a/crates/router/src/configs/settings.rs
+++ b/crates/router/src/configs/settings.rs
@@ -88,7 +88,7 @@ pub struct Settings {
     pub api_keys: ApiKeys,
     #[cfg(feature = "kms")]
     pub kms: kms::KmsConfig,
-    #[cfg(feature = "s3")]
+    #[cfg(feature = "aws_s3")]
     pub file_upload_config: FileUploadConfig,
     pub tokenization: TokenizationConfig,
     pub connector_customer: ConnectorCustomer,
@@ -716,7 +716,7 @@ pub struct ApiKeys {
     pub expiry_reminder_days: Vec<u8>,
 }
 
-#[cfg(feature = "s3")]
+#[cfg(feature = "aws_s3")]
 #[derive(Debug, Deserialize, Clone, Default)]
 #[serde(default)]
 pub struct FileUploadConfig {
@@ -848,7 +848,7 @@ impl Settings {
         self.kms
             .validate()
             .map_err(|error| ApplicationError::InvalidConfigurationValueError(error.into()))?;
-        #[cfg(feature = "s3")]
+        #[cfg(feature = "aws_s3")]
         self.file_upload_config.validate()?;
         self.lock_settings.validate()?;
         self.events.validate()?;
diff --git a/crates/router/src/configs/validations.rs b/crates/router/src/configs/validations.rs
index 569262d0d21..0b286ece843 100644
--- a/crates/router/src/configs/validations.rs
+++ b/crates/router/src/configs/validations.rs
@@ -127,7 +127,7 @@ impl super::settings::DrainerSettings {
     }
 }
 
-#[cfg(feature = "s3")]
+#[cfg(feature = "aws_s3")]
 impl super::settings::FileUploadConfig {
     pub fn validate(&self) -> Result<(), ApplicationError> {
         use common_utils::fp_utils::when;
diff --git a/crates/router/src/core/files.rs b/crates/router/src/core/files.rs
index 13c4d3dfdf3..f3e56489806 100644
--- a/crates/router/src/core/files.rs
+++ b/crates/router/src/core/files.rs
@@ -1,8 +1,8 @@
 pub mod helpers;
-#[cfg(feature = "s3")]
+#[cfg(feature = "aws_s3")]
 pub mod s3_utils;
 
-#[cfg(not(feature = "s3"))]
+#[cfg(not(feature = "aws_s3"))]
 pub mod fs_utils;
 
 use api_models::files;
@@ -29,9 +29,9 @@ pub async fn files_create_core(
     )
     .await?;
     let file_id = common_utils::generate_id(consts::ID_LENGTH, "file");
-    #[cfg(feature = "s3")]
+    #[cfg(feature = "aws_s3")]
     let file_key = format!("{}/{}", merchant_account.merchant_id, file_id);
-    #[cfg(not(feature = "s3"))]
+    #[cfg(not(feature = "aws_s3"))]
     let file_key = format!("{}_{}", merchant_account.merchant_id, file_id);
     let file_new = diesel_models::file::FileMetadataNew {
         file_id: file_id.clone(),
diff --git a/crates/router/src/core/files/helpers.rs b/crates/router/src/core/files/helpers.rs
index 818067207f4..9205d42aeee 100644
--- a/crates/router/src/core/files/helpers.rs
+++ b/crates/router/src/core/files/helpers.rs
@@ -31,33 +31,33 @@ pub async fn get_file_purpose(field: &mut Field) -> Option<api::FilePurpose> {
 }
 
 pub async fn upload_file(
-    #[cfg(feature = "s3")] state: &AppState,
+    #[cfg(feature = "aws_s3")] state: &AppState,
     file_key: String,
     file: Vec<u8>,
 ) -> CustomResult<(), errors::ApiErrorResponse> {
-    #[cfg(feature = "s3")]
+    #[cfg(feature = "aws_s3")]
     return files::s3_utils::upload_file_to_s3(state, file_key, file).await;
-    #[cfg(not(feature = "s3"))]
+    #[cfg(not(feature = "aws_s3"))]
     return files::fs_utils::save_file_to_fs(file_key, file);
 }
 
 pub async fn delete_file(
-    #[cfg(feature = "s3")] state: &AppState,
+    #[cfg(feature = "aws_s3")] state: &AppState,
     file_key: String,
 ) -> CustomResult<(), errors::ApiErrorResponse> {
-    #[cfg(feature = "s3")]
+    #[cfg(feature = "aws_s3")]
     return files::s3_utils::delete_file_from_s3(state, file_key).await;
-    #[cfg(not(feature = "s3"))]
+    #[cfg(not(feature = "aws_s3"))]
     return files::fs_utils::delete_file_from_fs(file_key);
 }
 
 pub async fn retrieve_file(
-    #[cfg(feature = "s3")] state: &AppState,
+    #[cfg(feature = "aws_s3")] state: &AppState,
     file_key: String,
 ) -> CustomResult<Vec<u8>, errors::ApiErrorResponse> {
-    #[cfg(feature = "s3")]
+    #[cfg(feature = "aws_s3")]
     return files::s3_utils::retrieve_file_from_s3(state, file_key).await;
-    #[cfg(not(feature = "s3"))]
+    #[cfg(not(feature = "aws_s3"))]
     return files::fs_utils::retrieve_file_from_fs(file_key);
 }
 
@@ -134,7 +134,7 @@ pub async fn delete_file_using_file_id(
     match provider {
         diesel_models::enums::FileUploadProvider::Router => {
             delete_file(
-                #[cfg(feature = "s3")]
+                #[cfg(feature = "aws_s3")]
                 state,
                 provider_file_id,
             )
@@ -235,7 +235,7 @@ pub async fn retrieve_file_and_provider_file_id_from_file_id(
                 diesel_models::enums::FileUploadProvider::Router => Ok((
                     Some(
                         retrieve_file(
-                            #[cfg(feature = "s3")]
+                            #[cfg(feature = "aws_s3")]
                             state,
                             provider_file_id.clone(),
                         )
@@ -365,7 +365,7 @@ pub async fn upload_and_get_provider_provider_file_id_profile_id(
                 ))
             } else {
                 upload_file(
-                    #[cfg(feature = "s3")]
+                    #[cfg(feature = "aws_s3")]
                     state,
                     file_key.clone(),
                     create_file_request.file.clone(),