Create new DMOD class for subset of config details from NextGen realization config

[robertbartel]

Create new, serializable DMOD class, similar in purpose to NgenRealization from ngen.config package. It should be composed of classes from ngen.config as well. The class will represent job config details provided by user, but it will not required certain information required by a NextGen realization config that DMOD can automatically determine.

The prime example is forcing configuration details, since these are subject to the details of the associated DMOD forcing dataset.

[aaraney]

For history sake, this issue surfaced out of conversation in #251.

[robertbartel]

Changing the status of this issue to Blocked. Much of the work is done and pushed to the i/post_agu22/5/request_config branch in my fork. However, it really needs the Pydantic work (#279) finalized and committed first.

[robertbartel]

This is no longer blocked.

After getting back into this, it looks like it might now make more sense to finish the Pydantic stuff in #279 first. The implementation I have thus far has an intermediate serialized state expected to be generated by Pydantic at the GUI but not aware of it at this level, which isn't ideal.

There needs to be some more (fairly complicated) rebasing done for #279, though. Going to give that a shot first, and if it looks too complicated, I will return to this in its less refined first form, which we can improve later.