Add Clippy support for Rust linting

[tjohnson-prometheum]

I saw there was rustfmt support, but I didn't see any support for rust's official linter: clippy

[jose-elias-alvarez]

Isn't this supported by the Rust language server? If so there's no point in routing it through null-ls, since it's strictly worse to use a CLI vs. an actual language server.

[choznerol]

Yes it is. The config is "rust-analyzer.check.command": "clippy".

ref: https://rust-analyzer.github.io/manual.html#clippy