Fix: VM connector does not start when run locally

[odesenfans]

Problem: launching the VM connector with run_vm_connector.sh yields
an exception because of issues with the return types of the API
endpoints.

Solution: remove Response and StreamingResponse type hints from
return values as they are not Pydantic models.

[odesenfans]

Two commits, one fixes documentation issues and the other fixes the actual bug. The issue occurs when running bash docker/run_vm_connector.sh on main. I got the following exception:

Process SpawnProcess-1:
Traceback (most recent call last):
File "/usr/local/lib/python3.9/multiprocessing/process.py", line 315, in _bootstrap
self.run()
File "/usr/local/lib/python3.9/multiprocessing/process.py", line 108, in run
self._target(*self._args, **self._kwargs)
File "/usr/local/lib/python3.9/site-packages/uvicorn/_subprocess.py", line 76, in subprocess_started
target(sockets=sockets)
File "/usr/local/lib/python3.9/site-packages/uvicorn/server.py", line 59, in run
return asyncio.run(self.serve(sockets=sockets))
File "/usr/local/lib/python3.9/asyncio/runners.py", line 44, in run
return loop.run_until_complete(main)
File "/usr/local/lib/python3.9/asyncio/base_events.py", line 647, in run_until_complete
return future.result()
File "/usr/local/lib/python3.9/site-packages/uvicorn/server.py", line 66, in serve
config.load()
File "/usr/local/lib/python3.9/site-packages/uvicorn/config.py", line 471, in load
self.loaded_app = import_from_string(self.app)
File "/usr/local/lib/python3.9/site-packages/uvicorn/importer.py", line 21, in import_from_string
module = importlib.import_module(module_str)
File "/usr/local/lib/python3.9/importlib/init.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "", line 1030, in _gcd_import
File "", line 1007, in _find_and_load
File "", line 986, in _find_and_load_unlocked
File "", line 680, in _load_unlocked
File "", line 850, in exec_module
File "", line 228, in _call_with_frames_removed
File "/opt/vm_connector/main.py", line 67, in
async def download_message(ref: str) -> Union[Dict, Response]:
File "/usr/local/lib/python3.9/site-packages/fastapi/routing.py", line 661, in decorator
self.add_api_route(
File "/usr/local/lib/python3.9/site-packages/fastapi/routing.py", line 600, in add_api_route
route = route_class(
File "/usr/local/lib/python3.9/site-packages/fastapi/routing.py", line 405, in init
self.response_field = create_response_field(
File "/usr/local/lib/python3.9/site-packages/fastapi/utils.py", line 87, in create_response_field
raise fastapi.exceptions.FastAPIError(
fastapi.exceptions.FastAPIError: Invalid args for response field! Hint: check that typing.Union[typing.Dict, starlette.responses.Response] is a valid Pydantic field type. If you are using a return type annotation that is not a valid Pydantic field (e.g. Union[Response, dict, None]) you can disable generating the response model from the type annotation with the path operation decorator parameter response_model=None. Read more: https://fastapi.tiangolo.com/tutorial/response-model/