feat(web-analytics): Add overview stats

[robbie-c]

Problem

Continuing web analytics

Changes

Add a new query for some overview stats
Move shared parts of some queries into a common file
Fix an issue with the pathname cte when there weren't any pageview events
Add an extremely basic grid layout, which is still very much WIP

(the next step will be improving the UI)

How did you test this code?

(Behind FF) ran it

[mariusandra]

Overall looks good, just some suggestions to get this in line with out frontend guidelines.

[mariusandra]

I still believe you're over-engineering it with the CSS grid (e.g. did you think of mobile? we have had many problems with the grid on dashboards, etc...), and it would be better for everyone to just do:

<div className='space-y-2'>
  <div className='flex flex-col gap-2'>
    <div className='w-50 sm:w-full md:w-full'>{first_one}</div>
    <div className='w-50 sm:w-full md:w-full'>{second_one}</div>
  </div>
  <div>{third one}</div>
</div>

or something like that and call it a day.

Since this is feature flagged, I'll 🤷 now, but this will come back.