feat: Full patch separation support (#572)

This PR adds explicit patch support. A user can set `separatePatchReleases` to true and receive not only major/minor updates but also patch updates separately. This functionality is also implicitly enabled if `automerge` is set to `patch`.
This PR also enables separate major/minor/patch configuration, e.g. config overrides for major versions, for patch versions, etc. `branchName` is currently overridden for patch branches using this technique.

Closes #390, Closes #538