Docs: Add RepositoryService usage and function from SQLAlchemyPlugin

[MONIER-ChE]

Summary

Adding two more chapter on Documentation as @cofin said :

cofin: please feel free to open an issue re: the docs.  When i first wrote the tutorial, the service layer didn't exist in advanced alchemy.  But now that it's there, we need to update them to show how it layers on top.
cofin: basically, I'd like to make 2 more chapters to the tutorial:
1) using service and repositories together
2) using dtos, services, and repositories together

Basically, RepositoryServices are the place for binding "buisness logic" or specific things link to our project here that operates on a repository object

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