feat: removing customerId from platformExternalAccount request (#218)

### TL;DR

Added a new `PlatformExternalAccountCreateRequest` schema with a
`platformAccountId` field and updated the platform external accounts
endpoint to use this new schema instead of the generic
`ExternalAccountCreateRequest`.

### What changed?

- Created a new `PlatformExternalAccountCreateRequest` schema that
includes a `platformAccountId` field for platform-specific account
identification
- Updated the platform external accounts POST endpoint to reference the
new schema
- The new schema maintains the same required fields (`currency` and
`accountInfo`) as the original but adds the optional `platformAccountId`
field

### How to test?

- Test the platform external accounts creation endpoint with the new
`platformAccountId` field
- Verify that existing requests without `platformAccountId` still work
as expected
- Confirm that requests with `platformAccountId` properly store and
reference the platform's identifier

### Why make this change?

This change allows platforms to associate their own internal account
identifiers with external accounts, enabling easier account management
and reference within their own systems while maintaining compatibility
with the existing API structure.

Author: pengying

mintlify/openapi.yaml

@@ -0,0 +1,15 @@
+type: object
+required:
+  - currency
+  - accountInfo
+properties:
+  currency:
+    type: string
+    description: The ISO 4217 currency code
+    example: USD
+  platformAccountId:
+    type: string
+    description: Your platform's identifier for the account in your system. This can be used to reference the account by your own identifier.
+    example: ext_acc_123456
+  accountInfo:
+    $ref: ./ExternalAccountInfoOneOf.yaml

openapi.yaml

@@ -79,7 +79,7 @@ post:
     content:
       application/json:
         schema:
-          $ref: ../../components/schemas/external_accounts/ExternalAccountCreateRequest.yaml
+          $ref: ../../components/schemas/external_accounts/PlatformExternalAccountCreateRequest.yaml
         examples:
           usBankAccount:
             summary: Create external US bank account