New metric: `ceph_crash_reports` which counts the entries returned by
`ceph crash ls` by daemon name and archival status.
This is not the same as `ceph_new_crash_reports` which is the value of
the `RECENT_CRASH` health check, and that only counts the non-archived
errors of the past two weeks. The new metric counts errors as long as
they are not purged (which is done after 1 year by defaults).
Xavier Villaneau