R2: provide baseline stage-in capability (not dependent on caching)

[pymonger]

The stage-in capability shall be a single-point executable/script that has capability to support the following use cases:

• stage in data from an HTTP/HTTPS URL (allowing allowing authentication to URS)
• stage in data from an S3 URL (allowing authentication via AWS access/secret keys or unsigned requests)
• stage in data from MAAP API via collection-concept-id and readable_granule_name

Definition of Done:

• [x] stage_in.py script that handles the above use cases
• [x] CWL documents that demonstrate the above use cases
• [x] Documentation provided
• [x] Github repo commits provided
• [x] Live demo provided

[pymonger]

Implemented at https://github.com/pymonger/stage_in.

[jjacob7734]

Final design at https://docs.google.com/presentation/d/1bTMKPRAeioxsKv7okcvWYjIbXoynmB8T8H2bL3vzYLU/edit#slide=id.g14535295eac_0_7