`documents`: Allow for SQLLite WASM backend

[marcus-pousette]

Problem
Currently you run into RAM usage problem when having many documents because the document store index is in memory. Additionally, the query performance is very bad if there are many documents

Solution
Use SQLLite WASM as an alternative backend together with OPFS storage

TODO

• Make abstraction around index search engine
• Implement a SQLLite WASM engine for this engine abstraction

#274

[marcus-pousette]

Blocked by sqlite/sqlite-wasm#48

Looking for alternatives how to glue this together to work in all envs

[marcus-pousette]

Way forward
For browsers: wa-sqlite
For node native: sqlite3