Docker compose (closes Issue #2)

Changes:

• A docker compose.yml is used to fire up the container.
• The compose YAML has two optional environment variables (OVERRIDE_CATALOG_URL and USE_OVERRIDE) which allows one to override the catalog URL hardcoded in the dockerfile. This is helpful to firing up a server pointing to a test STAC, as currently the production STAC is empty. The test STAC I have it pointed to also contains OSN data, which allowed me to verify that everything was working w/o having AWS credential in the container.
• The build.py file was modified to look for the two optional variables, but will still work fine without running via docker compose up.
• Other changes were discussed in the previous MR and accepted today.

Upon review and acceptance, the dockerization branch will be deleted. Let's get a full review in before we accept!

Note: Some of the changes discussed accidentally slipped into an open MR !3 (merged) that was accepted/merged by @ewojtylko1. Therefore the changes shown are more limited, however, the changes that slipped in the last MR were not documented there hence I documented them here.

Remaining issues:

• Issue #6 is relevant - right now the compose.yml expects a image tag of "zarr-to-opendap" to exists.