Remove duplication between Ci::Config::Entry::Service and Image
In !26149 (comment 295921988) we removed the inheritance Service < Image
because of a refactoring that was conflicting with it.
Because of that we had to inline the common parts. In the Ci::Config::Entry
s we should use modules to remove duplication instead of inheritance because it can cause issues with the DSL that automatically defines helper methods.
We should remove duplication the same way it was done with Ci::Config::Entry::Processable
.