enhancement request: make it easier to replace MongoDb

Currently Huly uses MongoDb for primary storage. Ideally the storage can be abstracted so that it can be replaced with a different database.

We use Postgres exclusively. To match the flexibility of MongoDb, we plan to use the Apache Age extension that turns Postgres into a Cypher graph database.

After a text search for `mongo` in the codebase, it seems like most of the references are in the `server` directory. References in `pods` are are configuration, understandably.

However there's a few in `/packages/collaborator-client` and `/packages/text-editor` that should be abstracted away.