[blob] Add CLI option to run cleanup task

Summary:
Resolves ENG-4759.
Added CLI subcommand to choose if we want to start blob service server or run the cleanup task.

Depends on D9355

Test Plan:

• Existing CLI options for running server work the same - not providing any option starts the server
• cargo run -- server works the same vay as above
• cargo run -- cleanup starts the cleanup task

Reviewers: michal, varun, jon

Reviewed By: michal

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9413