[backup] Update backup dockerfile

Summary:
ENG-4513
Very similar to the report service dockerfule from D9037.

Depends on D9040

Test Plan: docker compose build backup-server, tested on staging if it works

Reviewers: bartek, patryk, kamil, jon

Reviewed By: bartek, jon

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9063