Formalize the schema for raptor.Master.submit_workers() *descr* parameter.

[eirrgang]

The expected fields have been evolving for the dictionary passed as the descr argument to rp.raptor.Master.submit_workers(). Before the expected and allowed fields in the dictionary evolve further, it would be helpful to define a data structure or type hinting for this aggregate.

I think the RCT TypedDict would suffice, and the subclass docstring would be a good home for the notes currently in the submit_workers() docstring.

Also note that environment and pre_exec are currently optional fields, but are not mentioned in the submit_workers() docstring.

[andre-merzky]

This will be addressed as part of #2684

[andre-merzky]

This is now a proper TaskDescription and thus strongly typed - see #2892

[mturilli]

@eirrgang can we close this?

[eirrgang]

It is my understanding that this will be resolved when #2892 is merged. If there are remaining ambiguities, I believe they will be just documentation bugs that can be easily addressed in follow-up.