Support scheduled backups

[bohdan-shulha]

Users will be able to specify the period of backup job launch.

Need to implement an execution of the specified schedule.

How do I see it right now:

1. Users will specify the backup options on the service edit page.
2. Ptah will create corresponding Docker Services (mode = job) with an initial scaling 0.
3. Ptah's scheduler will put the 'scale service' task at the specified intervals to run the backup job.

The execution tracking will be out of the MVP scope, but, most probably, should have to be done via monitoring for the container's events: https://docs.docker.com/engine/api/v1.46/#tag/System/operation/SystemEvents

The ReplicatedJob creates a new container when the job starts and this container lives until the job is finished.

[bohdan-shulha]

Replaced with a simpler to integrate process in #65.