feat: Floating Tags

[apricote]

It would be nice if releaser-pleaser could automatically maintain tags for only the major and minor versions. This helps for example in GitHub Actions where users might want to use v1.x.x compatible versions.

• When tagging v1.1.2, releaser-pleaser should also update the floating tags v1 and v1.2 to the same commit
• When tagging a pre-release, releaser-pleaser should not move the floating tags. They are reserved for stable versions

Once this is implemented, we can also update the GitHub tutorial to use the floating tag: docs/tutorials/github.md.