Add repository check script

Packaging repositories for downstream forks should have a consistent layout. Check what we did manually before.

$ ./check-pureos-pkg-repo -u https://source.puri.sm/Librem5/debs/pkg-phosh.git


Summary for https://source.puri.sm/Librem5/debs/pkg-phosh.git
=============================================================

OK:   Default branch is 'pureos/byzantium'
OK:   Branch 'pureos/byzantium' is protected
OK:   pristine-tar branch present
OK:   Branch 'pristine-tar' is protected
OK:   CI enabled
OK:   Snipptes disabled
OK:   Wiki disabled
OK:   Merge method is fast-forward

There's clearly more that can be checked and we need to cater for pureos/{master,latest} in the puros space but that can be done as follow ups.

I also have a script that does most of the setup which i need to clean out.