fix(playlist-plugin): expose playlist plugin version

Expose the plugin version by adding a `VERSION` property to the constructor, to
retrieve the version of the component on a given player simply do:

```javascript
// Retrieve the player
const player = document.getElementsByTagName('video')[0].parentElement.player;
// Print the component version
console.log(player.pillarboxPlaylist().version());
```

packages/pillarbox-playlist/src/pillarbox-playlist.js

@@ -1,4 +1,5 @@
 import videojs from 'video.js';
+import { version } from '../package.json';
 
 /**
  * @ignore
@@ -469,6 +470,7 @@ export class PillarboxPlaylist extends Plugin {
   }
 }
 
+PillarboxPlaylist.VERSION = version;
 PillarboxPlaylist.prototype.options_ = {
   autoadvance: false,
   repeat: false