Need a way to trigger GHA ci for PRs that don't change the code, but change the infra itself

[jiridanek]

Ideas

• when changing infra code (Makefile, YAML gha workflows, helper scripts, ...) always rebuild everything in PR
• same when changing tests that are stored in tests/ directory but they may test multiple or all images
• leave it as it is, now all images are rebuilt on push to a PR branch in PR submitter's fork, if they enabled gha there
• allow triggering jobs on demand with a PR comment, something like is possible with openshift-ci
  • RHOAIENG-19051: chore(Makefile): remove dependency on bin/buildinputs for running image tests #948 (comment)
• trigger some image builds always on every PR, either random, or pick the "interesting" ones that give broad coverage of our CI capabilities, e.g. codeserver is interesting one