[clang-tools-extra] [clang-tidy] Add ClangQueryChecks config option (PR #123734)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL requested changes to this pull request.

Additionally:
- more detailed documentation needed (entire section in documentation)
- i would name it CustomChecks instead
- need protection against check name conflicts, and maybe some protection for adding checks for current modules ? Maybe enforce "custom-" as prefix ?

Idea is fine, require some work.

https://github.com/llvm/llvm-project/pull/123734