Add a workflow to keep meta-package versions in sync

[LeoColomb]

Better than on roots/wordpress as it keeps the workflow logic all in the same place.

Closes previous attempts (sorry for the noise!):

• Add workflow for tag propagation on meta-package #537
• Add a workflow to keep meta-package versions in sync wordpress#42

Closes roots/wordpress#1

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A bit more explanations:

• It has an input to be able to dry-run for debugging before actual tags submission.
• It makes the diff based on tags listed throught GitHub Repo API.
• It pushes the tags on the meta-package repo (has to be done as a loop, via the matrix).
• It submits a release to properly resolves Automatically make highest tag the latest release wordpress#1.

[swalkinshaw]

Might be worth writing a local action in JS for this, but let's give this a try anyway 🚀

[retlehs]

🚀 Looks good. Thanks for the breakdown!

[LeoColomb]

@swalkinshaw Might or might not 😁
That was my goal: try to avoid creating and maintaining a new GitHub Actions (local or not), and be sure to write as little code as possible.
The workflow ended to be quite large (😭), but at least there is no code files left here and there "just" to keep tags in sync.

I hope this is going to be stable enough to stay as simple as that 🤞