Completely automate the release process

[Thesephi]

Currently, a Release cycle involves:

1. creating & merging a release PR (e.g. release/X.X.X)
2. creating a new git tag (e.g. vX.X.X)
3. using the GitHub interface to create a new Release
4. then GitHub actions will automatically publish to npm & GitHub Packages registries

As seen above, only step (4) is automatic. Would be cool if steps (2) and (3) are also automated. Only step (1) should remain manual as it needs code reviewer approvals.