Add example showing enabling interactivity

[marcoscaceres]

Add an example that shows how to enabling interactivity.

[zachernuk]

we have syntax in the explainer today - would it be a good idea to begin building out/hosting pages that would expect to run these examples as well as the syntactic description? I guess that's kind of the job of tests as well. (also I think "interactivity" as discussed in 2022 is more like the stagemode="orbit") /facetoface

[AdaRoseCannon]

Chairs to make Model-Sample repo

[Yonet]

@zachernuk @AdaRoseCannon we have the repo https://github.com/immersive-web/model-element-samples

[AdaRoseCannon]

Thank you for creating that :)