feat: Cargo support design document

This commit introduces Cargo supporting package manager design
and also contains information about the direction of future work
on support for Rust-based Python extensions.

Co-authored-by: Bruno FS Ciconelle <[email protected]>
Co-authored-by: Bruno Pimentel <[email protected]>
Signed-off-by: Alexey Ovchinnikov <[email protected]>

Author: 2 people