Separate redis and rabbitmq from site docker-compose

[timbeccue]

Description

docker-compose-site.yml currently defines redis and rabbitmq services. At deployment sites, these services already run on the host machine, so banzai shouldn't manage them.

Changes

1. Extract redis and rabbitmq into a separate compose file. Sites that need them (local dev, testing) can run both compose files together. Production sites that already have redis/rabbitmq just run the main file.
2. Make redis and rabbitmq connection details configurable via environment variables. Currently the connection URLs are hardcoded to docker-internal hostnames. These should be configurable so sites can point at their own instances.
3. Remove depends_on references to redis and rabbitmq since they may not be defined in the same compose file.