[client-backup] add argon2 dependency

Summary:
ENG-4512.

We will use this crate as a key derivation function (KDF) for hashing a password with BackupID.

Test Plan: cargo build in native_rust_library

Reviewers: michal, marcin, ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8884