Create test-specific 🐳 file

[michplunkett]

Related to:

• https://github.com/lucyparsons/OpenOversight/issues/1054

Description of Changes

Creating a test-specific 🐳 Docker file. This will be the first step in implementing PostgreSQL in the testing environment so that we can get a true 1:1 comparison between the environments.

Tests and linting

• [x] This branch is up-to-date with the develop branch.
• [x] pytest passes on my local development environment.
• [x] pre-commit passes on my local development environment.