feat: Add push-artifacthub action, push artifacthub files to artifacthub branch

[viccuad]

Description

Relates to https://togithub.com/artifacthub/hub/issues/2922

Test

Tested from viccuad@github-actions and consumed by https://github.com/viccuad/allowed-fsgroups-psp-policy

See these 4 runs for main and 0.1.9:

• triggered by main, test.yml workflow: https://github.com/viccuad/allowed-fsgroups-psp-policy/actions/runs/4502885701 no changes
• triggered by main, relese.yml workflow: https://github.com/viccuad/allowed-fsgroups-psp-policy/actions/runs/4502885737 Creates the :latest image. Skips check-artifachub step, as versions may be different, skips push-artifacthub job, as we don't want to commit the artifacthub-pkg.yml changes.
• triggered by 0.1.9 tag, test.yml worfklow: https://github.com/viccuad/allowed-fsgroups-psp-policy/actions/runs/4502950922 no changes
• triggered by 0.1.9 tag, release.yml workflow: https://github.com/viccuad/allowed-fsgroups-psp-policy/actions/runs/4502950913 Creates the :v0.1.9 image, does check-artifacthub, does push-artifacthub

The same for runs for main and 0.1.10.

The repo has an artifacthub branch: https://github.com/viccuad/allowed-fsgroups-psp-policy/tree/artifacthub

The policy appears signed in artifacthub: https://artifacthub.io/packages/viccuad/test-policy/allowed-fsgroups-psp there, version 0.1.9 is missing metadata & readme because I forgot to update artifacthub-repo.yml with ID. Version 0.1.10 should all be fine. Next check for 0.1.10 will happen at 18:34 UTC approx. In 20 mins after this PR was open.

Additional Information

Tradeoff

Potential improvement

[viccuad]

tagged as v3.0.5

[viccuad]

deleted tag v3.0.5, tagged as v3.1.0, with a commit that consumes v3.1.0 too.