Allow environment config of HTTP proxy for auth server connection (#299)

You can set `HTTP_PROXY` on the container/host level, see https://docs.aiohttp.org/en/stable/client_advanced.html#proxy-support

custom_components/auth_oidc/tools/oidc_client.py

@@ -372,6 +372,7 @@ class OIDCClient:
             tcp_connector_args["ssl"] = ssl_context
 
         self.http_session = aiohttp.ClientSession(
+            trust_env=True,
             connector=aiohttp.TCPConnector(**tcp_connector_args)
         )
         return self.http_session