Add CLANG Tidy as a CI step

[blaisb]

Description

Our current CI has a check for GCC warnings, but this is clearly not as deep as the tests done by clang tidy. I am adding a new CI step to check the code using clang tidy. Right now this will throw some warnings and errors which I will fix progressively.

Testing

This is actually adding tests, so I am using this PR as a testing environment.
Code related list:

• All in-code documentation related to this PR is up to date (Doxygen format)
• Lethe documentation is up to date
• New feature has unit test(s) (preferred) or application test(s), and restart files are in the generator folder
• The branch is rebased onto master
• Changelog (CHANGELOG.md) is up to date
• Code is indented with indent-all and .prm files (examples and tests) with prm-indent

Pull request related list:

• Labels are applied
• There are at least 2 reviewers (or 1 if small feature) excluding the responsible for the merge
• If this PR closes an issue or is related to a project, it is linked in the "Projects" or "Development" section
• If the fix is temporary, an issue is opened
• The PR description is cleaned and ready for merge