Create batch_queue_flux stub

[dblitt]

Proposed Changes

This PR creates a stub batch_queue module for the Flux Framework. I will be working in the immediate future to implement the submit, wait, and remove functionality of this module so Makeflow and vine_factory will be able to natively submit jobs to a flux instance. batch_queue_flux is currently marked as experimental.

I also have fixed some out of date documentation in batch_queue.h

Merge Checklist

The following items must be completed before PRs can be merge.
Check these off to verify you have completed all steps.

• make test Run local tests prior to pushing.
• make format Format source code to comply with lint policies. Note that some lint errors can only be resolved manually (e.g., Python)
• make lint Run lint on source code prior to pushing.
• Manual Update Update the manual to reflect user-visible changes.
• Type Labels Select a github label for the type: bugfix, enhancement, etc.
• Product Labels Select a github label for the product: TaskVine, Makeflow, etc.
• PR RTM Mark your PR as ready to merge.

[tphung3]

Ok, this is a good template for further work. I think you know Flux enough by now to implement batch_queue_flux_submit and batch_queue_flux_remove. Don't worry about supporting all features, and instead try to submit basic Linux commands to flux and remove them using above APIs. To test your work you can write a custom test script calling batch_queue_flux_submit and batch_queue_flux_remove.