[clang-tools-extra] Rename CODE_OWNERS -> Maintainers (PR #114544)

[Julian Schmidt via cfe-commits]

https://github.com/5chmidti approved this pull request.

LGTM in regard to my details.

There are some emails that have their `@` escaped. Was that intended?

https://github.com/llvm/llvm-project/pull/114544