mod_http_admin_api: Ensure freshness of metrics when in manual mode When in manual collection mode, as recommended for Prometheus, collection needs to be triggered manually, or they would be stale, possibly dating from the start of the server. This might vary per metric depending on how and when the metrics are gathered.

This module discards typing notifications sent to a bare host JID,
preventing error replies to be sent. These errors are harmless but can
be annoying sometimes if your client shows them prominently.