* Watcher: fix metric stats names
The current watcher stats metric names doesn't match the current
documentation. This commit fixes the behavior of `queued_watches`
metric, deprecates `pending_watches` metric and adds `current_watches`
to match the documented behavior. It also fixes the documentation, which
introduced `executing_watches` metric that was never added.
Fixes#34865
There is currently no way to see what user executed a watch. This commit
adds the decrypted username to each execution in the watch history, in a
new field "user".
Closes#31772