[llvm] [libc++] Add Docker images to support incoming pre-merge CI transition (PR #144597)

[via llvm-commits]

cmtice wrote:

@ldionne I think we need this file in the llvm-zorg repository (where we configure the premerge runners): https://github.com/llvm/llvm-zorg/tree/main/premerge .  Do you have access to that repo?

https://github.com/llvm/llvm-project/pull/144597