BlenderBot2 interactive_web: Object of type AverageMetric is not JSON serializable

[justquick]

Patch description
Simply cast the model_response['metrics'] values as plain ints instead of AverageMetric objects so model_response can be JSON serialized.

Testing steps
Running the following command

$ parlai interactive_web --task blended_skill_talk:all -mf zoo:blenderbot2/blenderbot2_400M/model --search-server http://localhost:5000

Open localhost:8080 when the interactive_web task comes online. Put in a message and post and backend gets this traceback:

Traceback (most recent call last):
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/socketserver.py", line 316, in _handle_request_noblock
    self.process_request(request, client_address)
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/socketserver.py", line 347, in process_request
    self.finish_request(request, client_address)
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/socketserver.py", line 360, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/socketserver.py", line 720, in __init__
    self.handle()
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/http/server.py", line 427, in handle
    self.handle_one_request()
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/http/server.py", line 415, in handle_one_request
    method()
  File "/Users/jquick/Projects/ParlAI/parlai/scripts/interactive_web.py", line 202, in do_POST
    json_str = json.dumps(model_response)
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/Users/jquick/.pyenv/versions/3.8.7/lib/python3.8/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type Av

Other information
This is what the chunk of model_response looks like before the change

'metrics': {'clen': AverageMetric(5),
            'ctrunc': AverageMetric(0),
            'ctrunclen': AverageMetric(0)}

And after

'metrics': {'clen': 5,
            'ctrunc': 0,
            'ctrunclen': 0}

Now interactive_web page is working and can chat w/ bot

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[stephenroller]

Thanks for the contribution. Instead, could you please change it instead to:

json.dumps(model_response.json_safe_payload())?

[justquick]

Ah, didnt know that was a thing, im new to this but finding it very useful. Fixed & tested

[klshuster]

thanks for the fix!

[stephenroller]

Thanks for the fix!