Add support for Rust Cargo.toml dependency vizualisation to file blob view

What does this MR do?

This MR adds support for the Cargo.toml dependency file within the blob view, including dependency linking. Cargo is the package manager used in the Rust eco-system, a rapid growing programming language and a quite active package registry.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

backend: This MR makes use of the already existing toml-rb Gem, which was already in used but marked as optional.

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team