Cleanup of CI/CD

This MR implements an iteration on Continuous Integration and Delivery.

• Consolidate test stage
• Merged install_test_dependencies into a common .test-job which is shared with test:unit and test:end-to-end.
• build: stage will now publish an image to the container registry. BUILD_IMAGE_NAME: "$CI_REGISTRY_IMAGE/$CI_COMMIT_REF_SLUG:$CI_COMMIT_SHA"
• test:unit: now uses the Docker image provided from the build stage, rather than running straight from source (this is good especially making sure the Docker container "works")
• test:end-to-end: Added a migration test, which is only a pass for now.

Next iterations

1. Traverse/Generate access tokens for both gitlab1 and gitlab2 instances
2. In test:end-to-end, we need to generate an appropriate config.json based on the services provided (gitlab1, gitlab2)

This is part of the enablement for the test-framework, also lays out the skeleton.