Convert check-format-commits.sh to use allowlist

Convert check-format-commits.sh to use allowlist

Initially check-format-commits.sh tried to check everything, using a
banlist to exlude files not appropriate for checking.

Its becoming clear that that approach isn't workable, given that the
number of files that we should not check far outweighs the number of
files that we should check.

Ideally we should be checking .c files, .h files and their .in
counterparts, everything else should be excluded (at least for now)

convert the script to using an allowlist, only checking the above list,
and ignoring everything else

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
(Merged from https://github.com/openssl/openssl/pull/24865)