Separate creating parallel command and running command

[altheaden]

Creating the command is now a process that can be called without running the command, for use when we wish to run the command elsewhere.

Checklist

• API documentation in the Developer's Guide (api.md) has any new or modified class, method and/or functions listed
• Testing comment in the PR documents testing used to verify the changes

[altheaden]

I tested this branch with the cosine bell suite, against a baseline, and everything ran as expected.

[xylar]

@altheaden, this is great! I'll test this now. Could you add a line just above or below this one:
https://github.com/E3SM-Project/polaris/blob/main/docs/developers_guide/api.md?plain=1#L302
that refers to the new function? That way, it will show up in the automatically generated docs.

[altheaden]

@xylar Sure, I noticed that there are some other un-updated functions in that file (e.g. get_available_cores_and_nodes instead of get_available_parallel_resources, should I update all of the functions for polaris.parallel.py?

[xylar]

@altheaden, yes, please do!

[altheaden]

@xylar done, let me know if there is anything else I need to do!

[xylar]

I ran the pr suite with this branch, comparing against a baseline of the current main and everything passed. Thanks @altheaden!