Add Sample of :internal Module

[esafirm]

Hey team! Thanks for this framework. I believe it benefits a lot of people, even those not directly using it!

Currently, in my project, we're still allowed to have :impl -> :impl dependencies. This :internal module might be the improvement we need. It would be great if you could provide a sample implementation of it.

Thanks!

[vRallev]

What exactly are looking for in the sample? It's really just a matter of adding a Gradle dependency from the :impl module on the :internal module. Do you think the documentation is lacking?

[esafirm]

Just curious about what kind of code belongs to :internal.
It's also the only type of module that's missing from the sample project.

[vRallev]

Basically what the docs say:

:internal modules are used when code should be shared between multiple :impl modules of the same library, but the code should not be exposed through the :public module. This code is internal to this library.

This is often helpful when you have multiple implementations of the same API, but they share some code. E.g. we have multiple apps that sometimes use different implementations.