Git migration: addition of pipeline and gitignore

[Johnny Jazeix]

Hi,
I've added a pipeline to check the po files using msgfmt to all
added/updated files on commits.
In svn, it was a pre-commit hook preventing the push but we cannot do
the same in Git so it is a pipeline that will check, either on MR or
on commits on master that the po files are correct.
The script is in
https://invent.kde.org/sysadmin/ci-utilities/-/blob/master/po-lint.sh?ref_type=heads,
maybe we can think of other steps in the pipeline for the future.

After discussion in
https://invent.kde.org/teams/localization/issues/-/work_items/1#note_1693853,
we also added a default .gitignore to all repos:
https://invent.kde.org/localization/l10n-af/-/blob/master/.gitignore?ref_type=heads.
If you think it makes sense to add more generic filters on all repos,
please tell so we can all benefit of it.

Cheers,
Johnny