doc/rados/configuration: Mention show-with-defaults and ceph-conf

A small improvement based on
"Why is it still so difficult to just dump all config and where it comes from?"
https://lists.ceph.io/hyperkitty/list/[email protected]/thread/EZSLRYBYEWDA6YIARQVMUKQUWHAE3PGR/

`show-with-defaults` is very useful, and `ceph-conf` is mentioned
so that it's clear that it's legacy, and the user doesn't have to
wonder if it's actually useful but was forgotten in the list.

Signed-off-by: Niklas Hambüchen <[email protected]>

Author: nh2

doc/rados/configuration/ceph-conf.rst

@@ -519,6 +519,9 @@ The following CLI commands are used to configure the cluster:
   the command line or at runtime via admin socket, ``ceph tell``, or ``ceph daemon``
   commands. The source of each option value is displayed.
 
+* ``ceph config show-with-defaults <who>`` is like the above,
+  but also shows all defaults, and for changed values, where they are changed.
+
 * ``ceph config assimilate-conf -i <input_file> -o <output_file>`` ingests a
   configuration file from *input_file* and sets any valid options found into the
   Monitor configuration database. Any settings that are unrecognized, are
@@ -527,6 +530,8 @@ The following CLI commands are used to configure the cluster:
   useful when transitioning from legacy configuration files to centralized
   Monitor-based configuration.
 
+* ``ceph-conf --show-config`` is a legacy command.
+
 Note that ``ceph config get <who> [<option>]`` and ``ceph config show
 <who>`` will not necessarily return the same values. The former
 command shows only compiled-in default values. In order to determine whether a