Issue:
Bug: refactor: change primary key of payment_methods table for v2



## Description

Previously our payment_methods table had `id` as PKey. 
Which needs to be changed to a new Primary key namely `payment_method_id`.

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 -->
Changing the primary key of the payment_methods table from (id) to the payment_method_id.

### Additional Changes

- [ ] This PR modifies the API contract
- [x] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

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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
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Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd recommend starting with one first so the PR
can focus on the implementation (unless it is an obvious bug or documentation fix
that will have little conversation).
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Required for api_v2 migration

## How did you test it?
<!--
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 Db id migration, doesn't requires any specific testing

## Checklist
<!-- Put an `x` in the boxes that apply -->

- [ ] I formatted the code `cargo +nightly fmt --all`
- [ ] I addressed lints thrown by `cargo clippy`
- [ ] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible


Testing:

Just Db id migration, doesn't requires any specific testing

Patch:
diff --git a/crates/diesel_models/src/schema.rs b/crates/diesel_models/src/schema.rs
index b8c5344cbbb..55f8e935b14 100644
--- a/crates/diesel_models/src/schema.rs
+++ b/crates/diesel_models/src/schema.rs
@@ -934,7 +934,7 @@ diesel::table! {
     use diesel::sql_types::*;
     use crate::enums::diesel_exports::*;
 
-    payment_methods (id) {
+    payment_methods (payment_method_id) {
         id -> Int4,
         #[max_length = 64]
         customer_id -> Varchar,
diff --git a/crates/diesel_models/src/schema_v2.rs b/crates/diesel_models/src/schema_v2.rs
index 164600c88ac..90046d3fd95 100644
--- a/crates/diesel_models/src/schema_v2.rs
+++ b/crates/diesel_models/src/schema_v2.rs
@@ -931,7 +931,7 @@ diesel::table! {
     use diesel::sql_types::*;
     use crate::enums::diesel_exports::*;
 
-    payment_methods (id) {
+    payment_methods (payment_method_id) {
         id -> Int4,
         #[max_length = 64]
         customer_id -> Varchar,
diff --git a/migrations/2024-07-22-082828_change_primary_key_for_payment_methods/down.sql b/migrations/2024-07-22-082828_change_primary_key_for_payment_methods/down.sql
new file mode 100644
index 00000000000..26dd04d739b
--- /dev/null
+++ b/migrations/2024-07-22-082828_change_primary_key_for_payment_methods/down.sql
@@ -0,0 +1,5 @@
+-- This file should undo anything in `up.sql`
+ALTER TABLE payment_methods DROP CONSTRAINT payment_methods_pkey;
+
+ALTER TABLE payment_methods
+ADD PRIMARY KEY (id);
diff --git a/migrations/2024-07-22-082828_change_primary_key_for_payment_methods/up.sql b/migrations/2024-07-22-082828_change_primary_key_for_payment_methods/up.sql
new file mode 100644
index 00000000000..5fc305bc92c
--- /dev/null
+++ b/migrations/2024-07-22-082828_change_primary_key_for_payment_methods/up.sql
@@ -0,0 +1,12 @@
+-- Your SQL goes here
+-- The below query will lock the payment_methods table
+-- Running this query is not necessary on higher environments
+-- as the application will work fine without these queries being run
+-- This query should be run after the new version of application is deployed
+ALTER TABLE payment_methods DROP CONSTRAINT payment_methods_pkey;
+
+-- Use the `payment_method_id` column as primary key
+-- This is already unique, not null column
+-- So this query should not fail for not null or duplicate value reasons
+ALTER TABLE payment_methods
+ADD PRIMARY KEY (payment_method_id);