contrib: Add release helper scripts for preparing micro releases

[joestringer]

Automate the preparation of micro releases via a set of scripts. Steps in this PR:

• Run start-release.sh to generate helm charts, authors, changelogs, etc. Provide target release version and GH project number for N+1 version.
• Inspect changes and create commit with name "Prepare for release vX.Y.Z".
• Run submit-release.sh to send PR for this commit
• Manually close the old GH project
• Review & merge PR
• Pull release branch for true version of release commit
• tag-release.sh to tag current release & push releases (requires GPG key)
• Continue other steps from templates

Backporting

For backports, the docs and GH issue template changes can be dropped, it's only useful to have the scripts.

[aanm]

LGTM, only a small thing missing.

[christarazi]

Thanks for PRing these! A few minor comments below. Do you intend to merge this when ready or wait to give them a whirl on the next release, then merge?

[joestringer]

Do you intend to merge this when ready or wait to give them a whirl on the next release, then merge?

I'm fine to go either way. No specific rush for this PR but if it's easier to iterate on the scripts in-tree then we can do so. I guess for ease of use we should also backport them to each branch so they're available locally (for those who don't have a separate Cilium git tree for each release).

[aanm]

I didn't look at the scripts. I'll try them out in the next release and see how they go 🎉