release: support 8.x releases

[v1v]

Motivation/summary

8.x is the base branch for running the releases from. main should be updated with the changelogs when a new minor and the mergify snippet.

For such, we are gonna use the backport merge policy with Mergify and create the PR to main with the backport-8.minor label, so once it's merged it will be backported automatically to the new minor branch.

This might be a bit chicken:egg problem, since the PR in main contains the changes in Mergify, but I expert Mergify to be clever enough to apply the new changes and the create the PR automatically....

Otherwise, we might need to create two PRs:

• one with the mergify changes
• another one with the changelog

So the first one needs to be merged first and the second one after.

Test

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

Related issues

[mergify]

This pull request does not have a backport label. Could you fix it @v1v? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label.