mgr/telemetry: reset health warning after re-opting-in

mgr/telemetry: reset health warning after re-opting-in

When telemetry requires re-opting-in (whenever new data
is available), a health warning is set by the module. This health
warning should be reset once the user re-opts-in (with `ceph telemetry
on`), but currently it might take longer. Fixing it here by waking up
serve() immediately after re-opting-in, which will
invoke refreshing health checks.

Fixes: https://tracker.ceph.com/issues/56486
Signed-off-by: Yaarit Hatuka <yaarit@redhat.com>
(cherry picked from commit b8bbf642c1bc985e5e08639f44adc0e0d7c686da)

Conflicts:
  src/pybind/mgr/telemetry/module.py
  Conflicts were due to the new opt-in flow which was introduced in
  Quincy.