Add workflow to automatically assign milestone

[westonruter]

This is a follow-up to:

• Add workflow to automatically add plugin labels #2484

We have labels to identify which plugin(s) an issue or pull request is associated with. For example, #2469 has:

Additionally, we have the milestone:

(In reality, a PR should be able to be associated with multiple milestones because we have a monorepo. This isn't possible, however.)

As of #2513 the labels are now automatically applied.

The plugin-specific milestone can also automatically be assigned based on which plugin has the most changed lines in the PR. This milestone could then change automatically as additional changes are pushed.

As a bonus, when the changelog is being gathered for a given plugin, in addition to looking at the PRs in a plugin's specific milestone, we should also see if there are any merged PRs with the plugin's label which are associated with an open milestone. These can automatically be included in the changelog as well. This solves a manual issue of needing to make sure that a single PR with changes for multiple plugins get a changelog entry in each.

[dilipom13]

Hello team,

I’m interested in helping with this issue (#2541).

I see PR #2586 already implements the milestone assignment workflow. I reproduced the same approach locally on branch maintenance/auto-plugin-milestone and verified:

• npm run test-unit-js (6 tests passing)
• npm run lint-js, npm run lint-json, npm run tsc

I’d prefer to collaborate on #2586 rather than open a duplicate PR. Please let me know if you’d like me to:

• help review/test Automatically assign plugin-specific milestones #2586 on wp-env, or
• push any small fixes (e.g. rebase, CI) to that PR.

Thanks.