Deprecated: use POST /plugins/app:{app}/add {task_id, request_id}. Make a link to connect the app a task is waiting on [write]

Deprecated: use POST /plugins/app:{app}/add {task_id, request_id}. Still served exactly as before; every answer carries a Deprecation header. For a task with an open connect_app request (see GET /tasks/{id}): a link the person the request is addressed to can open in any browser to connect the app. Native GitHub additionally requires that person to sign in to AgentSky before consent. Only that person can make it. The link can be used once, within fifteen minutes, and this is the only response that carries it; making another replaces one that was not used. When the app is connected the task continues by itself. Answers 404 when the task has no such open request, 403 request_not_yours when it is addressed to somebody else, and 503 not_migrated until the platform's link table is in place.