Allow to add simplified workers to services

[bohdan-shulha]

We've implemented "workers" as "processes" which are fully independent units.

This will cause lots of issues when users would like to have 2 and more workers with the exact same docker image, env variables, secrets, configs and so on.

Example - ptah-server itself. We need to serve: the Laravel Web App, the schedule:work command and queue:work to process the scheduled tasks themselves.

Need to allow to add the "Worker Command" to the service creation form, so that it will create multiple Docker Services per one process definition.

Workers must not share volumes and should not be able to map ports & caddy endpoints.

Ensure that workers can operate with in-line env variables to allow minimal customization, like this:

SPRING_PROFILES_ACTIVE=etl /path/to/executable

For the first version, let's omit everything except the command definition itself.