feat: add additional-paths property to manifest releaser

[jack-lewin]

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Fixes #1921 🦕

---

This PR adds an additional-paths property to the manifest releaser.

Additional paths are useful for monorepos where a package might depend files from other directories.

For example, if we want to trigger a release in apps/my-app-2 when commits are found in libs/my-lib:

apps/
    my-app-1
    my-app-2
libs/
    my-lib

{
  "packages": {
    "apps/my-app-1": {},
    "apps/my-app-2": {
      "additional-paths": ["libs/my-lib"] // additional-paths would be a new config option
    }
  }
}

Best reviewed commit-by-commit.

[jack-lewin]

Hi @chingor13, sorry for the nudge - are you still maintaining this project?
If not, is there anyone else I should reach out to?