[clang-tools-extra] [clangd] Enable config files by default in clangd-indexer (PR #228683)

[Nathan Ridge via cfe-commits]

https://github.com/HighCommander4 requested changes to this pull request.

The code changes look good, but let's mention this in the [release notes](https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/docs/ReleaseNotes.md#improvements-to-clangd) as well.

https://github.com/llvm/llvm-project/pull/228683