Allow users to specify which "main.py" to run in a computational service

[newton1985]

Describe the user role
As an osparc user, I would like to improve the process of running computational jobs.

Describe the goal
It would be nice if users could point to the exact script they would like to run in a computational job. Going by a naming convention is a bit brittle, and it's especially difficult when there are multiple files in a repository with the name "main" in them (common enough).

Describe the benefit
Easier integration with a range of python code that will be run non-interactively.

Additional context

[calys]

would letting the user specify the full command be a decent solution?

> python src/my_code.py --my-arg 42

If the command is not specified, the runner would default to executing the first main.py it finds...

[newton1985]

absolutely!