[clang-tools-extra] Add clang-tidy external examples (PR #106675)

[Julian Schmidt via cfe-commits]

https://github.com/5chmidti commented:

Great idea to add this. Although, we should be careful to not end up with abandoned projects. I sampled three from the page in Clang, and they had their last activity at around ~10 years. At that point, API's have changed. Either way, adding external examples is a good idea IMO
(I should clean up my external clang-tidy template that's still private :) )

https://github.com/llvm/llvm-project/pull/106675