Allow clicking on timeline images to open the full-size image

**Feature request summary**
I would like to be able to click on the images in the results page to be able to see what is being rendered first. As of right now, even if an element is rendered, the images are so small you can't see them.


**What is the motivation or use case for changing this?**

There are some times when there is jank that certain elements are being shown and it would help debug the issue if you could see the full-size image.

**How is this beneficial to Lighthouse?**

It makes it easier for developers working on performance to see exactly what the page is rendering at FP, FCP, etc, versus guessing.