Resolve "Backend Refactor: Entities and API DTOs"

I refactored the API and Entities into separate modules, they are now in the $PROJECT_ROOT/fda-metadata-db folder. Other changes:

1. Upgraded Spring Boot Parent 2.3.4 -> 2.3.10.RELEASE on all Java-based services
2. Spring Cloud now also SR8.Hoxton -> 3.0.1
3. Removed some unnecessary Maven code for dependencymanagement
4. Your DTOs and Entities now comply with the Java-standard CamelCase naming convention (no other changes in your code, just renaming)
5. All services have either implemented tests or mocks, they all are ready for test implementation

What should be fulfilled to be able to merge into dev

• Please check if the data store works, I did not change very much, but due to the high refactoring it can be the case that some runtime stuff does not work as you intended

Closes #42