Enhancement: Apply Photon image CDN to video posters

### Impacted plugin

Jetpack

### What

Could you add support for images in video posters to Jetpack?

For example, there is the following code:

```

```

### How

If Jetpack would automatically add `i0.wp.com` to the image files (e.g. `video-poster-image.jpg`) that relate to the video posters, that would be great. Since it would solve the problem of the drop in PageSpeed scores.

```

```

Right now this has to be done manually. But what if we disabled Jetpack? Then the links to the posters in the cloud won't work.

The issue does not name a file, test, or entry point. Start by locating Jetpack's Photon image URL handling and the code that renders or filters WordPress video poster URLs; verify the poster is rewritten through the image CDN while video URLs remain unchanged and behavior is safe when Jetpack is disabled.

Written by the indexing model from the issue text.