Test files should be updated to use a test database

Since mockDBConnection is no longer an option, the following changes should be made:

Tests should use a test database (probably using the same Postgres setup and credentials but using a different value for WARTHOG_DB_DATABASE). This can be done either using a separate .env file or by setting the variable in the test npm script.
- It would also be helpful to have a script to instantiate this db:
```
"bootstrap:test": "WARTHOG_DB_DATABASE=warthog-starter-test yarn db:create && WARTHOG_DB_DATABASE=warthog-starter-test yarn db:migrate",
```
project.integration.test.ts: Remove mockDBConnection from getServer() call
testHelpers.ts: deleteTempDB() helper function should be replaced with either running yarn db:drop or hard-deleting the Project created in the integration test. The calls to it in globalSetup.ts and globalTeardown.ts should be removed.

goldcaddy77 / warthog-starter