Make `MauiCommunityToolkitMvvmEventsBinder` extensible to other elements

### Problem Statement

Nowadays lots of developers are using third party libraries components which have their own `Command` properties which can use the MVVM command objects.

`AddCommunityToolkitIntegration` should provide a way to attach to those additional properties.

### Solution Brainstorm

```
options.AddCommunityToolkitIntegration(integration => {
integration.AddCommandSupport(
MyThirdPartyElement.RefreshCommandProperty,
MyThirdPartyElement.ValidateCommandProperty
)
});
```

Internally this is stored as `Dictionary` which we can leverage in the event binder.