Add Matomo page view tracking for the documentation

[bouweandela]

Description

Add Matomo page view tracking. This will allow us to report the number of users to demonstrate how relevant our software is to funders.

I've configured it without cookies and with respecting viewers who indicate they do not wish to be tracked for now. The documentation lives here: https://developer.matomo.org/guides/tracking-javascript-guide and I used these instructions for the integration with the pydata sphinx theme: https://pydata-sphinx-theme.readthedocs.io/en/stable/user_guide/static_assets.html

This also adds the footer with legally required information used in the ESMValTool docs since ESMValGroup/ESMValTool#4072.

Related to #2520

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Checklist

It is the responsibility of the author to make sure the pull request is ready to review. The icons indicate whether the item will be subject to the 🛠 Technical or 🧪 Scientific review.

• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
• 🧪 and 🛠 Documentation is available
• 🛠 All checks below this pull request were successful

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.62%. Comparing base (c53de2f) to head (2915470).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2955   +/-   ##
=======================================
  Coverage   95.62%   95.62%           
=======================================
  Files         266      266           
  Lines       15601    15601           
=======================================
  Hits        14918    14918           
  Misses        683      683           

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[valeriupredoi]

more Stuxnet 😁