Create a privacy-preserving landing page analytics roadmap for S123

Following on from the discussion which started in the July 2022 narrative report ticket, we need to discuss next steps for implementing a method to collect the number of visitors per S123 landing page.

Copy-pasting the 4 steps suggested by @rhatto to plug Clean Insights (which is based on Matomo and built by The Guardian Project):

1. Frontend modifications into the existing landing page code to plug Clean Insights JS SDK.
2. Consider that this will need some consent UX.
3. Setting up Clean Insights Infrastructure in a new virtual machine (and maintaining that machine).
4. Making sure that landing page deployments from the same service always use the same siteId (so stats will be gathered no matter how many mirrors exists and where they're hosted).

I made the issue confidential but I don't believe it needs to be!

cc: @rhatto