Rust: Add first class support for the Rust language and its related tool chains

Description of the feature request

Add support for the Rust programming language and the related tool chains such as Cargo and Rustup.

Use case / for what or how I would use it

The project scanner could recognize Rust code and enable support for the rust, rustup and cargo commands. This would enable existing rust projects to build seamlessly on Bitrise and could be particularly helpful to iOS and Android developers.

Justification

Rust was voted the 3rd most loved language in the 2015 stack overflow developer survey and has been number 1 in every survey, since. It is growing in popularity, particularly among fast-moving industries like cryptocurrencies and mobile app development. Mobile developers are using it as an alternative to C++ for cross-platform code, allowing complex portions of business logic to be written in one place and shared across Android, iOS & Web.
From a product perspective, adding Rust support also makes good business sense for Bitrise. Having first-class support for a language loved by Developers would generate goodwill. It would give the impression that Bitrise is in tune with the Developer community while making marketing materials more enticing to the tech leads who influence adoption. At the bottom line, this is a low-effort yet high-reward feature.

Thanks for the great suggestion @zmobile :slight_smile: