Introduce docker context fixtures

Summary:
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