Rust: be able to enable features like "derive" on serde

[thomasjm]

https://serde.rs/derive.html

https://doc.rust-lang.org/cargo/reference/features.html

[thomasjm]

• Support this in a sample environment
• Add a test in the sample environment
• Add features stuff to the init.evcxr file
• Get the test passing
• Be able to add schemas to kernel packages
• Add "string list" to schemas
• Put it all together in the UI