Test Project feature (#2162)

### ❔What, Why & How

This new feature brings the concept of test projects to AL-Go for
GitHub. The purpose of this is to allow the user to split building and
testing into separate projects. This can be especially useful if some
tests are unstable and might require a re-run to succeed. In such
scenarios, it's nice not to have to wait for compilation again.

A test project is a special type of project that depends on one or more
regular projects. It will download and install artifacts from those
dependent projects and run all test apps it finds. It allows any
customization or settings used in regular projects, such as build modes
or conditional settings. The only limitation is test projects are not
allowed to build apps.

Related to issue: #

### ✅ Checklist

- [x] Add tests (E2E, unit tests)
- [x] Update RELEASENOTES.md
- [x] Update documentation (e.g. for new settings or scenarios)
- [ ] Add telemetry

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Co-authored-by: spetersenms <spetersenms@users.noreply.github.com>