add syndic_user option in the master config

salt/files/master.d/f_defaults.conf

@@ -1116,6 +1116,8 @@ ext_pillar:
 # LOG file of the syndic daemon:
 {{ get_config('syndic_log_file', 'syndic.log') }}
 
+# The user under which the salt syndic will run.
+{{ get_config('syndic_user', 'root') }}
 
 #####      Peer Publish settings     #####
 ##########################################