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
8187515aab