Fix mentions of the updated metrics in docs

Author: chrzaszcz

Diff for: doc/operation-and-maintenance/Logging-&-monitoring.md

@@ -108,8 +108,8 @@ For time-based metrics, you can choose to display multiple calculated values for
 
 ```
 Session count:                   <prefix>.global.sm_total_sessions.count
-Outgoing XMPP messages:          <prefix>.<domain>.c2s_element_out.message_count.one
-Incoming XMPP messages:          <prefix>.<domain>.c2s_element_in.message_count.one
+Outgoing XMPP messages:          <prefix>.<domain>.xmpp_element_out.c2s.message_count.one
+Incoming XMPP messages:          <prefix>.<domain>.xmpp_element_in.c2s.message_count.one
 Successful logins:               <prefix>.<domain>.sm_session.logins.one
 Logouts:                         <prefix>.<domain>.sm_session.logouts.one
 Authorization time:              <prefix>.<domain>.backends.auth.authorize.<value-type>

Diff for: doc/rest-api/Administration-backend_swagger.yml

@@ -816,10 +816,10 @@ paths:
                   items:
                     type: string
                   example:
-                    - c2s_element_in.stanza_count
-                    - c2s_element_in.error_count
-                    - c2s_element_out.stanza_count
-                    - c2s_element_out.error_count
+                    - xmpp_element_in.c2s.stanza_count
+                    - xmpp_element_in.c2s.error_count
+                    - xmpp_element_out.c2s.stanza_count
+                    - xmpp_element_out.c2s.error_count
               global:
                 schema:
                   type: array