[8.x] ci(major-release): support run major release [0-9]+.0.0 (backport #15329)

[mergify]

Motivation/summary

Support an automated process to create new major releases from main.

At the moment, we use 8.x for running minor releases, but we will eventually won't need to do that but run patch releases from 8.x and minor releases from main.

This is just an automated process to help with the major releases, it behaves as minor releases but with the difference in the branch where things should be branched off or the support for the changelog/mergify thingy.

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

Major release

Given this PR, let's run the major-release target using my forked repository for the hypothetical release of 9.0.0.

$ gh pr checkout 15329
$ export GITHUB_TOKEN=$(gh auth token)
$ make major-release RELEASE_VERSION=9.0.0 PROJECT_OWNER=v1v RELEASE_TYPE=major

It created two PRs:

• 9.0: mergify v1v/apm-server#66
• 9.0: update docs, versions and changelogs v1v/apm-server#67
• for 8.x we create three PRs (two for main and one for 8.x)

and updated 9.0 -> main...v1v:apm-server:9.0

Minor release

Then I ran the same for a new minor release 8.19.0 - but i required to sync up 8.x

$ git checkout 8.x
$ git cherry-pick 4fb3bbaf749d93518bfae48dccb859d475107c09
$ gh pr checkout 15329
$ export GITHUB_TOKEN=$(gh auth token)
$ make minor-release RELEASE_VERSION=8.19.0 PROJECT_OWNER=v1v RELEASE_TYPE=minor

It created three PRs:

• 8.19: mergify v1v/apm-server#68
• 8.19: update docs, versions and changelogs v1v/apm-server#69
• 8.19: update docs v1v/apm-server#70

Related issues

Part of #13968

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This is an automatic backport of pull request #15329 done by [Mergify](https://mergify.com).