Investigate using in-memory postgres server instead of Docker

[jonnydgreen]

Is your feature request related to a problem? Please describe.

Docker can be overkill for testing postgresql and is a dependency that we would like to avoid. We also can't test in windows/macos in the CI so we lose confidence in our testing.

Describe the solution you'd like

No Docker.

Possible options:

• pg-mem

Describe alternatives you've considered

Keep Docker for now