Add analytics

[benjeffery]

From tskit-dev/tskit#960
This creates public analytics at https://tskit.goatcounter.com/

[benjeffery]

@jeromekelleher Not sure if you get notifications about the site repo. Assume you're ok with analytics data being public? It can be behind a secret key instead if we like.

[jeromekelleher]

Perfectly happy for them to be public.

However, we should discuss the privacy implications etc. Can you summarise the effect of this change please?

[benjeffery]

This change adds a script which sends data on every page view to "GoatCounter". https://www.goatcounter.com/

They describe themselves as "an open source web analytics platform available as a free donation-supported hosted service or self-hosted app. It aims to offer easy to use and meaningful privacy-friendly web analytics as an alternative to Google Analytics or Matomo"

It doesn't use cookies or store any identifying data, so doesn't need a GDPR notice on the webpages. Session tracking is done by a hash hash(User-Agent + IP) which is only stored in RAM for 8 hours. (Session tracking can also be turned off).

[jeromekelleher]

OK, SGTM. We should get more buy-in on this before merging though

[benjeffery]

Have discussed on slack and in person with a few folks now, merging.