[llvm] workflows: Rewrite build-ci-container to work on larger runners (PR #117353)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

Was just about to start hacking on this today. 😆 

Not too familiar with the depot runners. It seems like they're paid self hosted runners? Is the foundation paying for them?

`llvm-premerge-linux-runners` should also work and will point to self hosted runners on the GCP project handling premerge. We intend to use that runner set to run the transitioned premerge jobs once we migrate to GHA.

https://github.com/llvm/llvm-project/pull/117353