Add basic Rust tool chain

There is some value in adding a basic Rust tool chain to GitLab. Besides Rust gaining more traction as a popular programming language in the wider software development ecosystem, it also has some effects on one of our core technologies: Ruby.

• bundler gets support for a cargo builder https://github.com/rubygems/rubygems/issues/2726
• the Ruby+Rust ecosystem is growing (https://github.com/matsadler/magnus, https://github.com/oxidize-rb/rb-sys),
• there are many new libraries written in Rust that we eventually would like to integrate in upcoming features (https://crates.io/crates/yrs)
• there are existing libraries we use and that are ported to Rust: Migrate commonmarker to Rust

• Add a basic Rust environment and the tool chain to GDK
• Add a basic Rust tool chain (compiler) to our CI base images