Document the new log_modules_fully option

src/ejabberd_options_doc.erl

@@ -835,6 +835,12 @@ doc() ->
         desc =>
             ?T("The time period to rate-limit log messages "
                "by. Defaults to 1 second.")}},
+     {log_modules_fully,
+      #{value => ?T("Number"),
+        note => "added in 23.xx",
+        desc =>
+            ?T("The modules listed in this option will log everything "
+               "independently from the general loglevel option.")}},
      {max_fsm_queue,
       #{value => ?T("Size"),
         desc =>