os/bluestore/bluefs: Add write op count metrics.

os/bluestore/bluefs: Add write op count metrics.

There were already several metrics counting bytes written to the various
regions of bluefs but nothing counting ops.

Also add a sum of bytes written to match the read and new write count
metrics.

This provides more insight behind the cause of
https://tracker.ceph.com/issues/58530.

Signed-off-by: Joshua Baergen <jbaergen@digitalocean.com>
(cherry picked from commit b4ad3840c513a15a5828418b5a733ed959390845)