mgr/prometheus: introduce fetch_perf_counters_metrics module option

mgr/prometheus: introduce fetch_perf_counters_metrics module option

Fixes: https://tracker.ceph.com/issues/58164
Signed-off-by: Avan Thakkar <athakkar@redhat.com>
Introducing module option in prometheus module to enable/disable support for exporting ceph daemons
perf counters as prometheus metrics, by default this option will be disabled. The use case for this option
is in case if ceph-exporter deployment failed for any reason then user still can have option to fetch metrics
from promethues exporter.