create `clang-tidy` lint step

[scravy]

Introduce in the lint phase a clang-tidy step.

It should only complain about additions (otherwise there are a LOT clang-tidy warnings).

To be defined: Should it fail the build if it finds a clang-tidy violation in the added parts?

Implementation suggestion:

1. run clang-tidy on the project.
2. calculate diff. remove all clang-tidy warnings which are not part of the additions in the diff.
3. if there are warnings in this set, fail the build.