Collect and measure impact of image sizes improvements

[joemcgill]

Purpose

As part of #760, we should define some initial baseline metrics against which we can evaluate the impact of the project and decide how to report them over time.

To start, we have created an initial query of HTTPArchive data that shows the distribution of the sizes error and the the effect on wasted pixels per image caused by selecting the wrong source.

Additional tasks

• Create a Colab to collect metrics for image sizes improvements.
• Modify the original HTTPArchive query, to limit it to only images that are the LCP image.
• Correlate percentage of sites with LCP passing rates with sites with an LCP image with an incorrect sizes attribute resulting in wasted pixels.