Set up basic (non-sbt integrated) E2e test environment

[gregbrowndev]

To e2e test the application thoroughly, we should build and run the http4s Docker container and the PostgreSQL database container at the start of the e2e tests. This ensures we test the real application as a closed box.

We can follow the same approach as in the integration tests which set up the environment at the start of the test. This has a major drawback, each test will get its own server and DB container. However, we can optimise this by integrating the test environment into sbt, see #30.