[services][feature-flags] Introduce command line arguments

Summary:
Introduce two arguments: one with sandbox flag and one with localstack url.
Added some libs with the same versions as in the backup service.

Depends on D6664

Test Plan:
Print help message using feature-flags --help and check if all the arguments are included.
Change the arguments and check if printing them shows new values.

Reviewers: michal, bartek, jon, varun

Reviewed By: bartek, jon

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6666