pgstac workflow

Opening this issue to keep moving on creating a custom pgstac image that will be used for pygeoapi's STAC API.

@ewojtylko1 - I added some scripts to a pgstac-workflow branch in the .gitlab/workflow folder. I see the general flow of this as:

1. generate_collections_json.py creates a collections.json file in a custom location. This is the slowest step because it traverses the whole catalog. I added some notes on ideas to optimize this step.
2. Use Dockerfile to spin up a pgstac image
3. pgstac_load.py loads the collections.json file generated above into the pgstac.

This is a general shell/outline. Sounds like you have some ideas on how to integrate this into a workflow that would ultimately get to our desired end result -- to publish this image somewhere & create a container with the most up-to-date data. pygeoapi will point to the latest container. I haven't created any of those workflows here, just the pieces that will likely fit into it.

Copying @aaufdenkampe_limno.com and @ttuhinanshu_element84.com for visibility and to help move this forward while I'm out of office.

I will also create a companion issue on the pygeoapi-builder repository for next steps for testing the STAC API.