Utility to run arbitrary commands on a container

Most projects need some kind of initialization. So far I am copy-pasting this kind of scripts all over the projects

```python
import pytest
import textwrap

@pytest.fixture(scope="session")
def backend_init(docker_services):

def backend_run(command):
docker_services._docker_compose.execute(
"run --rm backend " + textwrap.dedent(command))

backend_run("python -m django migrate")
backend_run("python -m django configure")
backend_run("""\
bash <