feat: Use Cappa by default

[pawamoy]

Cappa is 🔥

In some cases, the project will be CLI first, in that case there shouldn't be a cli extra.
But in other cases, the project will be library first, so we should probably put CLI dependencies (Cappa) behind a cli extra.

[pawamoy]

Nope, the way to handle CLI / no CLI is:

• if you start with a lib, just create a regular project
• if at some point you start offering a CLI, move code to a new projectlib, keep CLI in project
• users can install project (full) or projectlib (minimal)
• if you start a new project and know you will offer a CLI, create both project and projectlib