Add get_obs tasks to workflow using retrieve_data.py.

[christinaholtNOAA]

We need to have the lightning, LaRC, and metar datasets retrieved as part of the workflow. This requires the addition of new j-jobs and ex-scripts, and a new workflow metatask to retrieve each of them.

[christinaholtNOAA]

MIke is close to having a draft PR that will likely come after a couple of other tasks. Will work to integrate the task to stage data where the downstream tasks expect it.

[christinaholtNOAA]

@mkavulich and @christinaholtNOAA are going to join forces on getting the workflows for getting tasks and processing the data for the lightning and prepbufr.

The radar getting and processing will be done as a separate PR.

[christinaholtNOAA]

Addressed in PR #778