Convert forecast-only stage_ic job to python

[KateFriedman-NOAA]

What new functionality do you need?

The existing stage_ic job in forecast-only mode needs to be converted from shell to python. This should improve and enhance the job capabilities and make it more extensible.

This is a subtask of issue #2475.

What are the requirements for the new functionality?

Existing job functionality should be retained but converted to python and yaml.

Acceptance Criteria

Job still performs the same tasks.

TODO

• [x] update jobs/JGLOBAL_STAGE_IC to use .py version of ex-script
• [x] rename scripts/exglobal_stage_ic.sh to scripts/exglobal_stage_ic.py and convert to python
• [x] create ush/python/pygfs/task/stage.py and populate with defs for staging
• [x] create parm/stage and create yaml files within for each stage mode
• [x] check stage_ic job setup and dependencies

[KateFriedman-NOAA]

Will take care of as part of PR for issue #2475. Closing as not needed.