Call an app's API through a connection granted to this API key [write]

For a service holding an API key: app:<slug> only (422 not_callable otherwise). Calls url (https only, 400 https_required) through a connection of that app its owner granted to this key or to every key of the request's workspace (POST /plugins/{id}/share {workspace, api_key | all_api_keys}), exactly as POST /connectors/proxy: the workspace's tool-call rules decide first (403 capability_denied; 503 policy_unavailable), and a 2xx books one connector call to the key's account (native GitHub calls are free). connection_id names the connection when several of that app are granted (else 409 connection_required); 404 not_granted when none is. A browser session or a task pass is 403 key_required. Answers the third party's {status, ok, body}; 502 proxy_error when it could not be called.