ci: refactor workflows for release branching

[jescalada]

Closes #1517.

This refactors the release drafting and NPM publisher automation to work with release branches, as described in #1516. I've already updated #1516 with a step-by-step guide and a troubleshooting section based on my own testing.

Although it's a bit of a mess, I've replicated the release process in my git-proxy fork:

• Test releases made from drafts
• NPM test package built from those releases
• Related PRs showcasing the branching flow

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.21%. Comparing base (b6d72fc) to head (18a10be).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1520   +/-   ##
=======================================
  Coverage   90.21%   90.21%           
=======================================
  Files          69       69           
  Lines        5511     5511           
  Branches      944      944           
=======================================
  Hits         4972     4972           
  Misses        521      521           
  Partials       18       18           

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