feat: Adds opt-in support mp4 generation (refs sanity-io#10)

This update exposes a `mux-input.json` config file where users can opt-in to mp4 support. Polling behaviour has been updated to listen for static renditions completed on MUX's end. If a user has opted in, a small badge / reminder is  also displayed over the video input when static generation is still in progress.

1.0.1

1.0.0

0.3.4

1.0.1-beta.0

0.3.3

0.3.2

0.3.1

0.3.0