Nosql backend

[jonhealy1]

I am building a mongo backend for stac-fastapi here: https://github.com/jonhealy1/stac-fastapi-mongo
It still needs some work - transactions and core run and tests pass but other extensions need work, tlc. The way mongodb is setup could probably be improved if anyone knows anything about it. There are probably other things that need improvement or work too. I am no mongo expert.

[jonhealy1]

If anyone is interested there is an elasticsearch backend in development here: https://github.com/stac-utils/stac-fastapi-elasticsearch
A mongo backend is here: https://github.com/jonhealy1/stac-fastapi-mongo

[geospatial-jeff]

Closing this issue as we are moving backends out of this repo, ref #432