Keep repo key registered in alpine, and simplify Dockerfiles

[orgads]

Proposed changes

Simplify package installation in non-slim variants.

This can also be used in user images to install packages directly.

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• I have read the CONTRIBUTING document
• I have run ./update.sh and ensured all entrypoint/Dockerfile template changes have been applied to the relevant image entrypoint scripts & Dockerfiles
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation

[thresheek]

Hi @orgads !

We did that because we explicitely did not want the image to have the repository configured - as adding more packages with the repos configured might upgrade the packages to something newer than specified initially. This is also consistent with what we have for Debian-based images.

[orgads]

I see. I now changed it to just keep the key registered, but not register the repo. I see this is also done in debian. What do you say?

[orgads]

And simplified debian perl and otel to use the existing key too.

[thresheek]

Thanks @orgads !