Consistency between fallback of RequestValidation Middleware and Lifecycle

[AntoineDuComptoirDesPharmacies]

Problem

We notice that the fallback used in RequestValidation and Lifecycle are not aligned.

In RequestValidation:
The fallback is the first mime type defined in the openapi file if one is defined and if None, then it is "application/octet-stream".

In Lifecycle:
The fallback in case of missing Content-Type is "application/octet-stream".

This is resulting in some bugs when mime-type is not defined when request body is a JSON.
Indeed, in the following code, self.content_type equals "application/octet-stream" resulting in object "bytes" being returned :

  async def get_body(self):                                                                                                                                                                                                                                                                                         
      if is_json_mimetype(self.content_type):                                                                                                                                                                                                                                                                       
          return await self.json()                                                                                                                                                                                                                                                                                  
      ...                                                                                                                                                                                                                                                                                                           
      else:
          return await self.body() or None        

WSGI_0s - 0 0 - ERROR - api.provide.impl.magic_cart.controllers.manage_express_order_controller - 'bytes' object has no attribute 'buyer_id'
Traceback (most recent call last):
  File "/home/brultea/IdeaProjects/lcdp-magic-cart/api/provide/impl/magic_cart/controllers/manage_express_order_controller.py", line 26, in create_express_order
    buyer_id = express_order_creation_parameters.buyer_id
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'bytes' object has no attribute 'buyer_id'
AnyIO worker threads - 0 0 - ERROR - connexion.middleware.exceptions - HTTPException(status_code=500, detail="'bytes' object has no attribute 'buyer_id'")
AnyIO worker threads - 0 0 - ERROR - connexion.middleware.exceptions - HTTPException(status_code=500, detail="'bytes' object has no attribute 'buyer_id'")
MainThreads - 0 0 - INFO - uvicorn.access - 127.0.0.1:50613 - "POST /api/v1/express-orders HTTP/1.1" 500

This issue may be linked to #1269.

Proposal

In RequestValidation, if we fallback on a mime type located in the OpenApi file, then we should change the scope header "Content-Type" to match the fallback.