Support other document store

ODMantic is fantastic for my web services. I can focus on data structure definition, then persistence and async serving is super easy. However, the MongoDB license might be restrictive for commercial use.

Would you consider other document store such as CouchDB?

No files, tests, or entry points are named. Start by reviewing how ODMantic currently persists data through MongoDB, then investigate what a CouchDB-backed document store would require; done would mean a defined, working alternative store rather than only consideration of the idea.

Written by the indexing model from the issue text.