chore: add release utilities

[JamesHenry]

Description:

Demoed to Ben today. This PR adds release utilities for the rxjs repo. Ben will run yarn release locally which will version all the packages (currently just rxjs) and create a CHANGELOG.md entry, as well as create a GitHub release.

The release will act as a trigger for the publish GitHub workflow (which can also be triggered manually via the GitHub UI). It has also been configured to generate provenance data for npm (something which is only possible when publishing from GitHub actions like this)

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Additionally, creating the publish workflow involved adding a setup-node and install step again so I took the opportunity to create a shared composite action for this, and fix the node_modules caching to work for yarn across the board

[benlesh]

Overall, I'm very happy with these changes.

It would be very helpful for me if you could separately PR a small document about various useful commands. I think I'm good overall, but I won't have muscle memory for a bit.