refactor(core): allow referencing capabilities on the Tauri config file

[lucasfernog]

The current capability file design automatically adds all files in the capabilities folder to the application. While this is convenient for the developer, it restricts dynamic use cases (for instance plugins that are only enabled on debug or with an associated Cargo feature). After talking with @tweidinger we agreed we should add a reference on tauri.conf.json where the dev must specify which capabilities to include.

This PR adds a capabilities array inside app > security > capabilities where you can reference capabilities by identifier or inline capability objects (though this one isn't ideal since it lacks JSON schema support).

I'll open an issue later today detailing the dynamic capability implementation we can support.

[lucasfernog]

Maybe we should default to include all capabilities if the config array is empty? I know @FabianLars would like that so we won't deal with another "hidden" breaking change.

[FabianLars]

Yup, probably. But it's still beta so if it's objectively better than just break it 🤷

(i also don't really get the issue itself tbh so idk)

[lucasfernog]

I like how the latest change is a balance between DX and configurability.