Define use cases to facilitate community development

### Is your feature request related to a problem?

To facilitate community development, we need to propose use cases for smart contracts and for building DApps

### Describe the solution you'd like

Identify and specify the use cases that allow to enter the Archethic ecosystem easily

### Additional context

_No response_

The issue names no files, tests, or concrete entry points beyond smart contracts and DApps. Start by reviewing the Archethic ecosystem and agreeing on specific use cases and scope with maintainers; done means those use cases are clearly specified to help community members enter the ecosystem.

Written by the indexing model from the issue text.