Add ppc64el images and jobs
I am building packages for ppc64el and realized that Salsa pipeline didn't support it, so here is a merge request to add this feature.
Here is a test build of ppc64el packages of libntlm using this patched pipeline:
https://salsa.debian.org/jas/libntlm/-/pipelines/905060
As you can see also the aptly job works, publishing the ppc64el packages in its registry.
This merge requests depends on !627 (merged) first, so I'm marking this as draft until it has been merged.
If you need a ppc64el runner hooked up to salsa-ci-team/pipeline
(to re-generate images) just send me an encrypted registration token and I'll run the registration command on one of my ppc64el runners.