chore: set up multi-branch automated release

[mweberxyz]

Closes #3103

This relates to...

• automate releases #3042
• chore: automate releases with pr #3089

Rationale

An issue was identified in the automatic release logic, where the changelog generation did not take multiple live release branches and major versions into account.

In fixing, automated release of both 6.x from main and 5.x from v5.x is implemented, but will require two changes: this PR to main, and a corresponding change to v5.x.

Changes

• the Create Release PR workflow should always be run from main. A new input is required to say which release branch (currently main and v5.x) should the release be created for. The major and specific versions inputs have been removed, because a major version bump will necessitate changes to the release script and release workflow.
  • Read: whenever 7.0.0-alpha.1 comes around, ping me to update workflow to support major version bump and configuration across the three branches 😄
  • In case a non-linear version bump is needed, push the package.json version bump (either directly, or via PR) to main or v5.x and the release automation will run
• a given branch that deploys to a particular major version should have scripts/release.js file with two variables set in header of script: VERSION_TAG_PREFIX and BRANCH (implemented in this PR for main, and the corresponding for v5.x)
• getLatestRelease logic in scripts/release.js paginated and updated to only find the latest release for the given major version
• latest npm tag is explicitly being set in main releases

Demo

Create PR as a sample change and merge, then run create release PR workflow, merge PR, and observe releases
Note: both sample changes target package.json, neither triggered a release

	6.x.x	5.x.x
Sample change	mweberxyz#30	mweberxyz#31
Skipped release workflow	https://github.com/mweberxyz/nodejs-undici/actions/runs/8673906497	https://github.com/mweberxyz/nodejs-undici/actions/runs/8673905602
Create release PR
	https://github.com/mweberxyz/nodejs-undici/actions/runs/8673918032	https://github.com/mweberxyz/nodejs-undici/actions/runs/8673940346
PR	mweberxyz#32	mweberxyz#33
	https://github.com/mweberxyz/nodejs-undici/actions/runs/8673947634	https://github.com/mweberxyz/nodejs-undici/actions/runs/8673952207

NPM versions after demo runs: https://www.npmjs.com/package/@mweberxyz/undici?activeTab=versions
GitHub releases after demo runs: https://github.com/mweberxyz/nodejs-undici/releases

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Review ready

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.06%. Comparing base (ec74bf7) to head (c1b2ebf).
Report is 347 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3110      +/-   ##
==========================================
+ Coverage   94.04%   94.06%   +0.01%     
==========================================
  Files          89       89              
  Lines       24333    24327       -6     
==========================================
- Hits        22885    22883       -2     
+ Misses       1448     1444       -4     

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[mcollina]

These scripts are becoming incredibly complex. Can you add some tests for them with mocks?

[mcollina]

I don't think this will work when we cut v7. we should really use semver here instead of relying on filters.

[mweberxyz]

Yeah, I am not necessarily happy with the implementation, but wanted to get something up as fast as possible, knowing there's a ticking time bomb where a 6.x release following a 5.x release will cause corrupted release notes.

To give myself more time for a cleaner solution, I'll get a PR up with just a fix for that particular issue.