expose capability for site to talk to SIDE

[toddtarsi]

Something like this:

const talkToSIDE = async () => {
  const pluginChannel = await window.sideAPI.requestPluginChannel('your-plugin-id');
  if (pluginChannel) {
    pluginChannel.on('commandRecorded', (e) => { ... });
    pluginChannel.on('playbackStart', (e) => { ... });
  }
};