Have a web analytics platform like Matomo

Originally created by @sajolida on #12562 (Redmine)

Stuff we could do with an analytics platform:

Analyze our installation funnel. See where people are coming from, where people drop the most, etc.
Analyze navigation patterns in pages involved in tails#9814 (closed).
Analyze search engine requests (tails#11649 (closed)).
Analyze better the donation funnel.
Have better download stats (should be much easier with the new download page).
Maybe know which FAQ and Known issues are most frequent.
Have bits of info about where are people interested in Tails located in the world (especially on installation funnel).

Edited May 15, 2020 by sajolida