[clang-tools-extra] Allow to pass config file to clang-tidy-diff (PR #75457)

[Piotr Zegar via cfe-commits]

PiotrZSL wrote:

> Note: This file lacks a `SPDX-FileCopyrightText:` in the header. Is this on purpose?

Looks like llvm does not use SPDX-FileCopyrightText.
https://llvm.org/docs/DeveloperPolicy.html#copyright

As for change looks, fine but please update release notes entry in clang-tools-extra/docs/ReleaseNotes.rst

https://github.com/llvm/llvm-project/pull/75457