[BUG] [Flask] x-body-name is not in the right place to make Connextions work

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

Connexions only respects the x-body-name cfg when it's in the request body schema (or when it's in the schema of the referred type).

The existing AbstractPythonConnexionServerCodegen places it as the request body level.

The result is that there's not way to override the request body param name.

See also description here https://github.com/zalando/connexion/issues/757 which I've verified with the master build of this product.

openapi-generator version

master

OpenAPI declaration file content or url

Needs to look like this code for Connexions to use it...

 post:
      parameters:
      requestBody:
        content:
          application/json:
            schema:
              **x-body-name: overriddenParamName**
              $ref: '#/components/schemas/SomeType'
        required: true```


##### Related issues/PRs

https://github.com/zalando/connexion/issues/757 

##### Suggest a fix

Change the Python code gen to put it the right place

Start at AbstractPythonConnexionServerCodegen and inspect how x-body-name is emitted for Flask/Connexion request-body schemas; compare the generated declaration with the linked Connexion behavior. Done when the extension is placed on the request-body schema, including the referred type case, and relevant Python generator tests cover the generated output.