Feature: Async OpenFGA Client #854
Description
What are you trying to do?
Add get_async_client() method to OpenFGAContainer to support async OpenFGA clients.
Previous issue regarding OpenFGA with the initial contribution is: #806
Why should it be done this way?
Modern async web frameworks (FastAPI, async Django) use AsyncOpenFgaClient in production, but testcontainers only provides sync clients. This creates a production-test mismatch requiring ugly workarounds.
The OpenFGA SDK already provides both sync and async clients - testcontainers should support both.
Other references:
- [OpenFGA Python SDK async client docs](https://github.com/openfga/python-sdk#async-client)
- Similar pattern: Redis testcontainer provides both sync/async connections