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

[Louis Dionne via llvm-commits]

ldionne wrote:

Ack. I will say though that the inability for folks to see which Docker image we're using in the CI by just looking at the monorepo is a major usability and discoverability issue IMO. I don't want to slow down this migration by requesting a change at this time, but I would like us to revisit this once it is rolled out.

In the meantime, I'll close this since it looks like this file is now part of https://github.com/llvm/llvm-zorg/pull/474

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