[EAGLE-4453] Stream support

[luv-bansal]

What

• Support streaming endpoints GenerateModelOutputs or StreamModelOutputs from the stub
• Easier to setup client from env and just use it's stub like:

  
  from clarifai.client import BaseClient
  client = BaseClient.from_env()

advanced grpc users can use the stub directly from there.

stub = client.Stub response = stub.PostModelOutputs(...)

- Remove validation of app_id   as the base client

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### How
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