Support for the web-vitals framework#125

Not sure if it’s something that fits in with Plausible but it would be a nice addition to have a Web Vitals card in the dashboard that shows you stats (maybe over time?) about your web-vitality stats.

Link to framework: https://github.com/GoogleChrome/web-vitals/

Thank you for your contribution. We’re moving this thread to Github: https://github.com/plausible/analytics/issues/161