CI - run backend integration tests

[u-ways]

We now have containerised our integration tests to allow for cross-platform development regardless of environment which eliminates the need to constantly setup an active database service in our machines and avoid "it works on my machine" errors.

However, our CI is not setup to run the backend integration tests and so this ticket is to configure our CI to run the task:

- name: Backend Integration Tests
  run: ./gradlew integration 

This will involve some extra configurations on top of the two lines above to enable a database service container.

Here are some helpful resources:

• About continuous integration
• Creating PostgreSQL service containers