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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> I just no longer have the time needed to hold maintainer status. I'll still contribute as and when I have the time.

Thank you for your help! I'll move you to the inactive maintainers list, and if you find you have more time in the future to step back into a maintenance role, we'll happily move you back to active status.

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