Ignore private workspaces for versioning and changelogs

**Is your feature request related to a problem? Please describe.**

TLDR; Due to devs forgetting to apply labels we have private package changes appearing in changelogs which we don't want.

We use auto for publishing our npm monorepo of [Grafana developer tools](https://github.com/grafana/plugin-tools). Within this repo is a [private workspace](https://github.com/grafana/plugin-tools/blob/main/docusaurus/website/package.json#L4) for our documentation website. As it's private it never makes its way to NPM but occasionally (due to contributors not remembering to include the label we've configured for [omit-commits](https://github.com/grafana/plugin-tools/blob/main/.autorc#L13-L16)) our [changelogs include entries](https://github.com/grafana/plugin-tools/blob/main/CHANGELOG.md#mon-oct-28-2024) pointing to versions of the website.

**Describe the solution you'd like**

Not really sure how best to handle it but maybe we can provide an option to omit-commits (such as workspace name or package.json has `"private": true`) which would guarantee changes to a workspace never make their way into version calculations or the changelog?

**Describe alternatives you've considered**

**Additional context**