[infra] Simplify clang-tidy usage

[uilianries]

This PR "improves" the current usage of Clang tidy in the CI:

• First, it runs Cmake to obtain exported commands, which can be analyzed by clang-tidy
• Similar to the first, clang-tidy is now running in parallel with xargs -P
• Only errors from project headers are considered critical for failure
• When failing it will mark as failed, but will not break the CI. Which means it is optional, not a blocker

@ColinH @d-frey We could have it as technical debt, what do you think?

[ColinH]

Sounds good, with clang-tidy there's often that one check that you'd like to keep even if it has a false positive...