completion: complete more values of more 'color.*' configuration variables

Most 'color.*' configuration variables, with the sole exception of 'color.pager', accept the same set of values, but our completion script recognizes only about half of them. We could explicitly add all those missing variables, but let's try to reduce future maintenance burden, and use the catch-all 'color.*' pattern instead, so this list won't get out of sync when a similar new configuration variable accepting the same values is introduced [1]. Furthermore, their documentation explicitly mentions that they all accept the standard boolean values 'false' and 'true' as well, so list these, too, among the possible values. [1] OTOH, there will be a maintenance burden if ever a new 'color.something' is introduced which doesn't accept the same set of values. We'll see which one happens first... Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>