[services] Backup - Rust lib - Add terminate

Summary:
Depends on D4869

Adding terminating function in rust to be called from the c++.

The goal here is to:

• spawn a thread in rust that will listen on a thread-safe queue (initialize)
• schedule some data on this queue (process)
• gracefully exit the thread and release all resources (terminate)

Later on, in the spawned thread, we will connect to the blob service through the gRPC, but first things first.

I'm probably going to remove all logging before landing, I'm leaving it as is for now.

Test Plan:
In the c++ code:

#include "rust_lib/src/lib.rs.h"
// ...
extern "C" {
void rust_initialize();
void rust_process(const char *data);
void rust_terminate();
}
// ...
std::cout << "CALLING RUST CODE" << std::endl;
rust_initialize();
rust_process("aaa");
rust_process("bbbbb");
rust_process("cccccccccc");
rust_terminate();
std::cout << "CALLED RUST CODE" << std::endl;

Reviewers: tomek, varun, max, jon

Reviewed By: tomek, varun

Subscribers: ashoat, tomek, atul, abosh

Differential Revision: https://phab.comm.dev/D4870