busctl: rename --num-matches= → --limit-messages=

We should avoid unnecessary abbreviations for such messages, and this
puts a maximum limit on things, hence it should indicate this in the
name.

Moreover, matches is a bit confusing, since most people will probably
call "busctl monitor" without any match specification, i.e. zero
matches, but that's not what was meant here at all.

Also, add a brief switch for this (-N) since I figure in particular
"-N1" might be a frequent operation people might want to use.

Follow-up for: 989e843e75
See: #34048

shell-completion/bash/busctl

@@ -89,7 +89,7 @@ _busctl() {
                       --allow-interactive-authorization=no --augment-creds=no
                       --watch-bind=yes -j -l --full --xml-interface'
         [ARG]='--address -H --host -M --machine --match --timeout --size --json
-                      --destination --num-matches'
+                      --destination -N --limit-messages'
     )
 
     if __contains_word "--user" ${COMP_WORDS[*]}; then