messages: MForward: stash auth entity name

This will allow us to assess the entity name, used during auth, for a
forwarded request, which is otherwise unavailable to the receiving
party.

Fixes: #9913 (partially)
Backport: giant

Signed-off-by: Joao Eduardo Luis <joao@redhat.com>
mon: Monitor: stash auth entity name in session

Backport: giant

Signed-off-by: Joao Eduardo Luis <joao@redhat.com>
mon: Monitor: forward session entity name to leader

And populate mock session (for forwarded request) with forwarded entity
name.

Backport: giant

Signed-off-by: Joao Eduardo Luis <joao@redhat.com>
mon: Monitor: use session's entity name for audit log

Fixes: #9913
Backport: giant

Signed-off-by: Joao Eduardo Luis <joao@redhat.com>
Merge pull request #2944 from ceph/wip-9913

mon: auth entity name for forwarded messages

Reviewed-by: Sage Weil <sage@redhat.com>