add support for flat file like tinydb

[Barceloch]

I think that would be good idea add support for a flat file like tinydb in odmantic for use it in little projects using nosql... somethig like tortoise-orm that provide support for sql databases including sqlite...

something like:
engine = AIOEngine(system="aiotinydb", database="Name")
or
engine = AIOEngine(system="Motor", database="Name")