[lib][native] Add function to encrypt files

Summary:
Created a function that opens, encrypts and the saves a single media file.

Depends on D7224, D7222

Test Plan: Tested together with subsequent diffs where it is used

Reviewers: atul, marcin, kamil

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D7233