CE-587: Extend test coverage for ce template

The change includes repository-level integration tests and service-level unit tests for the main services.

I also introduced JaCoCo plugin as applied to the deployment backend. It version had to be upgraded to 0.8.8 due to Java 17 compatibility issues.

I also made equals, hashCode and toString functions for a couple of DTOs for testability.

Update: The service unit tests and repository integration tests have been merged into service integration tests. This gives more relevant functionality testing and more coverage. Also, the review comments have been resolved.