Support json + bytes type in multipart/form-data in RLC

[MaryGao]

In FaceAI we have bytes + json in form data, and we need to decide how to generate and support this in RLC.

https://github.com/Azure/azure-rest-api-specs-pr/pull/15710/files#diff-f87f0ee6317aecf95934a0e818d7f5fdc9dd5014fe9096e1403a5187d1581785R171

 @doc("Request of liveness with verify session creation.")
  model LivenessWithVerifySessionCreationContent {
      @doc("The content type for the operation. Always multipart/form-data for this operation.")
      @header("content-type")
      contentType: "multipart/form-data";
  
      @doc("The json for creating liveness session.")
      Parameters: LivenessSessionCreationContent;
  
      @doc("The image stream for verify.")
      VerifyImage: bytes;
  } 

  @sharedRoute
  @createsResource(LivenessWithVerifySession)
  createLivenessWithVerifySessionByFormData is Azure.Core.Foundations.ResourceCollectionOperation<
    LivenessWithVerifySession,
    LivenessWithVerifySessionCreationContent,
    LivenessSessionCreationResult,
    ServiceTraits>;

[qiaozha]

close it as supported.