log more changes made by chronyc commands

Log important changes from chronyc for auditing purposes.

Add log messages for:
- loaded symmetric keys and server NTS keys (logged also on start)
- modified maxupdateskew and makestep
- enabled/disabled local reference mode (logged also on start)
- reset time smoothing (logged also on clock steps)
- reset sources

sources.c

@@ -1546,6 +1546,8 @@ SRC_ResetSources(void)
 
   for (i = 0; i < n_sources; i++)
     SRC_ResetInstance(sources[i]);
+
+  LOG(LOGS_INFO, "Reset all sources");
 }
 
 /* ================================================== */