https_proxy env is ignored

[thoomasb]

It is currently not possible to use threema-gateway with a web proxy, as aiohttp does not check the $https_proxy environment variable unless it is explicitly told to do so.

See aiohttp documentation: https://docs.aiohttp.org/en/stable/client_advanced.html?highlight=proxy

threema-gateway could either allow to submit the web proxy setting as command line option and pass it to aiohttp, or it could use trust_env to let aiohttp use $https_proxy.

It works for me by changing gateway/_gateway.py and pass trust_env=True to aiohttp:

        self._session = aiohttp.ClientSession(connector=connector, trust_env=True)

That way, aiohttp is instructed to use $https_proxy.