CI: Add initial gitlab CI file

This patch will enable (not enforce) checking of APKBUILD files via
shellcheck. This of course can be expanded, but until #10689 is not
resolved, we should not enforce this.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
1 job for 10690-lint-apkbuild-files in 7 minutes and 30 seconds
Status Job ID Name Coverage
  Lint
passed #136
docker-alpine
shellscript_linting

00:07:30