Add media:content to rss feed

```
<item>
<title>Item 1</title>
<description>Sample Media RSS Item 1</description>
<media:content url="https://gihub.com/image1.jpg" type="image/jpeg" medium="image" duration="10"> </media:content>
</item>
```

Origin: https://wordpress.org/support/topic/open-graph-metadata-rss-feed/