Introduce docker context fixtures
Run every docker compose comand in its own context. This has a few
benefits over always using the default context:
- It better segregates our tests from the other stuff that we have running locally. For example, if a test adds an ECS local simulation context, we don't need to worry about naming collisions with an ECS local simulation context that might already exist.
- It provides an entrypoint through which to override context - for example, if we want to use an ECS local simulation context.
Test Plan: unit
Reviewers: johann, dgibson
Differential Revision: https://dagster.phacility.com/D8689