Adding mainline repo license to the Rust Cargo manifest files

Summary:
This diff introduces adding and fixing the license in the Rust Cargo manifest files inside the project.
The license is set according to the mainline repo license (@ashoat comment in D4534).

Test Plan: Running cargo b or cargo check produces no errors.

Reviewers: varun, karol-bisztyga, ashoat, jonringer-comm

Reviewed By: varun, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul, yayabosh

Differential Revision: https://phab.comm.dev/D4552