[llvm] [WIP][Github][CI] Add separate container for code-format premerge job (PR #161083)

[Baranov Victor via llvm-commits]

vbvictor wrote:

> > Prebuild binaries indeed is most straightforward and easy approach. BTW, do we have prebuild linux binaries available? I guess we need to download them from apt.
> 
> The release binaries on Github. Eg https://github.com/llvm/llvm-project/releases/tag/llvmorg-21.1.2 should have it. Apt doesn't allow precise control over minor versions.

I've implemented this solution. I think we better have a base container with prebuild tooling and then create `code-lint`, `code-format` on top of it.

As for the build size, here is what I got locally:
```
localhost/test-code-lint-container     latest      40a6e6950779  13 minutes ago  859 MB
localhost/test-code-format-container   latest      3552a9520deb  14 minutes ago  703 MB
```
Not great, not terrible :) I'll investigate if there is anything more to strip.

https://github.com/llvm/llvm-project/pull/161083