auth-config-ref.rst: fix signature keys

Fix names of cephx signature keys.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
filestore-config-ref.rst: mark some filestore keys as deprecated

Marked the following keys as deprecated since v0.65:
- filestore flusher
- filestore flusher max fds
- filestore sync flush

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #513 from dalgaaf/fix/wip-da-documentation

Fix documentation issues