prometheus: Handle the TIME perf counter type metrics

prometheus: Handle the TIME perf counter type metrics

This patch correctly sets the PERFCOUNTER_MASK to 3 so that the
PERFCOUNTER_TIME metrics are not ignored by the mgr_module code. It also
converts the TIME metrics from nanoseconds to seconds just like the ceph
perf dump does and exposes the metrics via prometheus module.

Signed-off-by: Boris Ranto <branto@redhat.com>
(cherry picked from commit 056bc08d51306f4e4d031d1e3ff68ad7312c55d8)

Conflicts:
	src/pybind/mgr/mgr_module.py: trivial resolution