Have a Rust PD in CellulOS

[sid-agrawal]

This is not immediately needed, and neither is it clear why it is needed. But if we decide to do this, we can look here:

• https://github.com/seL4/rust-sel4

It seems to example of

• Root Task written in rust where we do not use microkit.
• Other PDs written in rust where we do use microkit (I am assuming that the RootTask is non-rust)