feature request: make edgedb-py able to generate input models for insert/update queries

[iron3oxide]

As of now, edgedb-py generates a query function and a response model for a given query, but does not structure the input parameters in any way. This makes sense for most queries, but leaves a little to be desired on inserts and updates. It feels tedious to write a pydantic model containing all the fields that edgedb already knows about each time. Also, having to sync it to the query manually when there is a change in the query parameters adds maintenance cost.

I therefore propose that edgedb-py should be able to generate a pydantic input model for insert and update queries. This would make it perfect to use with FastAPI! This feature could be the new default or activated by a flag, depending on what makes more sense.

[iron3oxide]

Actually, now that I read #358, maybe it would make sense to be able to generate them for every kind of query? Would probably be less complex to implement too.