Support transactions

[siemova]

Please support transactions for atomic operations, as described here.

Ideally, Pydantic Mongo would expose the ability to start, commit, and/or rollback a transaction session. But, if not, at least enabling us to pass our own session object to repository methods should suffice.

[jefersondaniel]

I guess adding a session kwarg to the repository methods and passing it to the pymongo calls would work. What do you think?

I don't have time for doing it in the short term, but I will look into it when I have some time.