common,ceph: add output file switch to dump json to

common,ceph: add output file switch to dump json to

The `ceph tell mds.X cache dump` and `ceph tell mds.X ops` commands have a
useful `--path` argument that directs the daemon to save the dump of the output
to a file local the daemon. This has several advantages:

* We don't need to construct the JSON output in memory, which may be many gigabytes.
* Streaming writes to a local file is significantly faster than sending the data over the ceph messenger.
* The command spends as little time as possible holding relevant locks.

However, only some commands support this and we could make it generic to the
admin socket interface. So, add a generic --daemon-output-file argument to
achieve this.

The main concern with this is security (telling the daemon to write to
arbitrary files) but this is gated by the session caps which require
"allow_all" and that's typically only valid for the client.admin.

Fixes: https://tracker.ceph.com/issues/65747
Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>
(cherry picked from commit a3414684974380c1d335f1fcafc5245dbde1c0d6)