WIP doc: https://hackmd.io/@ondrejbudai/ryE_SGvx3

Goal:

• Ensure smooth enablement of Fedora 38 in the image builder stack.
• Remove all instances of Fedora 36 from our projects.
• Move Fedora workers to Fedora 38 (after CI is enabled)

Scope:

• rpmrepo definitions
• osbuild CI
• osbuild-composer image definitions and CI
• manifest-db
• image-builder distributions and CI
• koji-osbuild CI
• fedora workers

Acceptance Criteria:

• CI is fully enabled for Fedora 38.
• There are no traces of Fedora 36 in our codebase.

Open questions and notes:

• It would be great to clarify our testing policies (i.e. we fully test only on branched releases of Fedora, rawhide is best-effort)
• It would be great to write a step-by-step guide