This diff adds dependencies to the Rust `Cargo` manifest file for the notifications library wrapper.
Dependencies list:
tracing - Logging and tracing inside the functions.
tokio - Asynchronous calls.
lazy_static - Lazy static initialization that will be used for the Tokio runtime initialization.
a2 - APNS client library.
An empty services/tunnelbroker/rust-notifications/src/lib.rs file was added to prevent the build failures. This file will contain the Rust library code in follow-up diffs.
Linear task: [[ https://linear.app/comm/issue/ENG-1330/rust-notification-library-integration | ENG-1330 ]]