Instead of populating env vars, use Jupyter Settings interface

[grallewellyn]

EBS backed storage
Do for:
MAAP_API_HOST, WORKSPACE_BUCKET, DOCKERIMAGE_PATH_DEFAULT, and DOCKERIMAGE_PATH_BASE_IMAGE

Need to change extensions to read these from Jupyter Settings interface and change to initially be setting these items through Jupyter Settings interface

[marjo-luc]

The MAAP Jupyter server extension has been updated to leverage the Jupyter extension settings. Note that these changes are limited to the updates related to the OGC effort. See here for more details.