Issue:
Bug: [DOCS]: Add `X-Merchant-Id` to headers in Profile endpoints for v2 



### Description

We require `X-Merchant-Id` in the headers for the following endpoints in Profile:

- Profile - Create
- Profile - Update
- Profile - Retrieve
- Merchant Connector - List

We need to update the v2 API documentation.

Pull request description:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [x] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
Add X-Merchant-Id to headers in Profile endpoints for v2

### 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.

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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## 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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## 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`
- [ ] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible


Testing:

Patch:
diff --git a/api-reference-v2/openapi_spec.json b/api-reference-v2/openapi_spec.json
index 3f57faaf1d7..46c4868e4bd 100644
--- a/api-reference-v2/openapi_spec.json
+++ b/api-reference-v2/openapi_spec.json
@@ -711,6 +711,20 @@
         "summary": "Profile - Create",
         "description": "Creates a new *profile* for a merchant",
         "operationId": "Create A Profile",
+        "parameters": [
+          {
+            "name": "X-Merchant-Id",
+            "in": "header",
+            "description": "Merchant ID of the profile.",
+            "required": true,
+            "schema": {
+              "type": "string"
+            },
+            "example": {
+              "X-Merchant-Id": "abc_iG5VNjsN9xuCg7Xx0uWh"
+            }
+          }
+        ],
         "requestBody": {
           "content": {
             "application/json": {
@@ -767,6 +781,18 @@
             "schema": {
               "type": "string"
             }
+          },
+          {
+            "name": "X-Merchant-Id",
+            "in": "header",
+            "description": "Merchant ID of the profile.",
+            "required": true,
+            "schema": {
+              "type": "string"
+            },
+            "example": {
+              "X-Merchant-Id": "abc_iG5VNjsN9xuCg7Xx0uWh"
+            }
           }
         ],
         "responses": {
@@ -806,6 +832,18 @@
             "schema": {
               "type": "string"
             }
+          },
+          {
+            "name": "X-Merchant-Id",
+            "in": "header",
+            "description": "Merchant ID of the profile.",
+            "required": true,
+            "schema": {
+              "type": "string"
+            },
+            "example": {
+              "X-Merchant-Id": "abc_iG5VNjsN9xuCg7Xx0uWh"
+            }
           }
         ],
         "requestBody": {
@@ -864,6 +902,18 @@
             "schema": {
               "type": "string"
             }
+          },
+          {
+            "name": "X-Merchant-Id",
+            "in": "header",
+            "description": "Merchant ID of the profile.",
+            "required": true,
+            "schema": {
+              "type": "string"
+            },
+            "example": {
+              "X-Merchant-Id": "abc_iG5VNjsN9xuCg7Xx0uWh"
+            }
           }
         ],
         "responses": {
diff --git a/crates/openapi/src/routes/profile.rs b/crates/openapi/src/routes/profile.rs
index f726c76db84..fc56e642719 100644
--- a/crates/openapi/src/routes/profile.rs
+++ b/crates/openapi/src/routes/profile.rs
@@ -139,6 +139,13 @@ pub async fn profile_list() {}
 #[utoipa::path(
     post,
     path = "/v2/profiles",
+    params(
+        (
+            "X-Merchant-Id" = String, Header,
+            description = "Merchant ID of the profile.",
+            example = json!({"X-Merchant-Id": "abc_iG5VNjsN9xuCg7Xx0uWh"})
+        ),
+    ),
     request_body(
         content = ProfileCreate,
         examples(
@@ -169,7 +176,12 @@ pub async fn profile_create() {}
     put,
     path = "/v2/profiles/{profile_id}",
     params(
-        ("profile_id" = String, Path, description = "The unique identifier for the profile")
+        ("profile_id" = String, Path, description = "The unique identifier for the profile"),
+        (
+            "X-Merchant-Id" = String, Header,
+            description = "Merchant ID of the profile.",
+            example = json!({"X-Merchant-Id": "abc_iG5VNjsN9xuCg7Xx0uWh"})
+        ),
     ),
     request_body(
         content = ProfileCreate,
@@ -276,7 +288,12 @@ pub async fn routing_update_default_config() {}
     get,
     path = "/v2/profiles/{profile_id}",
     params(
-        ("profile_id" = String, Path, description = "The unique identifier for the profile")
+        ("profile_id" = String, Path, description = "The unique identifier for the profile"),
+        (
+            "X-Merchant-Id" = String, Header,
+            description = "Merchant ID of the profile.",
+            example = json!({"X-Merchant-Id": "abc_iG5VNjsN9xuCg7Xx0uWh"})
+        ),
     ),
     responses(
         (status = 200, description = "Profile Updated", body = ProfileResponse),
@@ -339,6 +356,11 @@ pub async fn routing_retrieve_default_config() {}
     path = "/v2/profiles/{profile_id}/connector_accounts",
     params(
         ("profile_id" = String, Path, description = "The unique identifier for the business profile"),
+        (
+            "X-Merchant-Id" = String, Header,
+            description = "Merchant ID of the profile.",
+            example = json!({"X-Merchant-Id": "abc_iG5VNjsN9xuCg7Xx0uWh"})
+        ),
     ),
     responses(
         (status = 200, description = "Merchant Connector list retrieved successfully", body = Vec<MerchantConnectorResponse>),