feat(init): no stop of service if source or resource dir is empty

[jmkerloch]

Need

For a better administration, a service could be loaded without any sources or resources.

Functionalities

• The service configuration has to contain a directory for sources et another for resources but those can be empty and road2 will not raise any error (only a warning).

Tasks

• [x] Code it
• [x] Modify tests inside test/functional/configuration/cucumber/features/conf-service.feature
• [x] Run tests inside docker (rtest, ctest, utest, itest)
• [x] Update docs (ex. functionalities.md, changelog.md)