Pagespeed overview: Default to 30 day window instead of 24 hours

First of all: Great product, exactly what I was looking for for our small e-commerce agency!

**Is your feature request related to a problem? Please describe.**

In the pagespeed overview, the histograms per check are displaying the past 24 hours. For use, and I guess for most people, it would make sense to view the past 30 days in the pagespeed overview, so that it is clear when pagespeed regression occured.

With the 24 hour histogram you **have to** view the pagespeed dashboard every 24 hours or you might miss a small regression. For example, if the pagespeed dropped from 95 to 70, but I view the dashboard in 2 days from now, I wont be able to see that the pagespeed dropped unless I remember that it was 95 before.

**Describe alternatives you've considered**
30 day window is visible in the detail, but this means opening each monitor.

I would be willing to create a PR if this is something you'd like to support

Start at the Pagespeed overview and inspect how its per-check histograms choose the current 24-hour window. Compare this with the existing 30-day window in the monitor detail view. Done means the overview defaults to 30 days, making regressions visible without opening each monitor.

Written by the indexing model from the issue text.