Java/Spring Docs: Recommendation section on organizing your app

[efgpinto]

While working on lightbend/kalix#7720 , I noticed it depends on the "Writing gRPC descriptors" where the contracts for implementing a value entity shopping cart are introduced and explained for the java counterpart. Obviously, for the spring-sdk such page does not make much sense (not entitled like that at least).

However, I think we could use that page (with an adequate title) to explain how do we expect the application to be organized (explaining the use of a domain package / records to hold the domain transformation logic, the entity as a wrapper of the domain, etc). I think it's a nice section to have before you dive in the details of implementing the different types of entities and it would allow us to have parity with the other sdk by using the value entity shopping cart as an example similar. Thoughts?

I don't have a title to propose yet though..

[beritou]

I think this is a great idea.

Suggestion: don't worry about the title now. Write the doc first and then we can find an appropriate title later.

[efgpinto]

Was discussing this with @franciscolopezsancho , @octonato and @aludwiko .

We've agreed that this page will be useful to explain some concepts although we also agreed to break the dependency between https://github.com/lightbend/kalix/issues/7720 and this section. Contents for this page is still up for refinement.