Add support for compiling Rust

Rust is fast becoming a requirement for Ruby-related projects:

1. Rust port of prometheus-client-mmap: gitlab-org/ruby/gems/prometheus-client-mmap!79 (closed)
2. Other gems like commonmarker
3. Ruby 3.2's YJIT

We should ship rustc with gitlab-omnibus-builder.

gitlab-org/build/CNG!1317 (merged) at least makes rustc available for the Ruby interpreter, but it does not cover 1 and 2 yet.

We want to make sure that adding Rust doesn't increase the image size of the final images. The gitlab-rails build implementation in Debian currently doesn't make it easy to pull in the gitlab-rust assets since the bundle install is intertwined with the final image. It should be straightforward for the UBI-8 image, though.