ci: add Plausible analytics to project website

[rich-iannone]

This PR sets up the docs site for Plausible analytics.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.61%. Comparing base (de3580d) to head (536dc89).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #806   +/-   ##
=======================================
  Coverage   91.61%   91.61%           
=======================================
  Files          47       47           
  Lines        5773     5773           
=======================================
  Hits         5289     5289           
  Misses        484      484           

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[rich-iannone]

From the site preview, we can see that the two <script> tags were added to the head (scan for plausible near the bottom):

In checking other pages, I see that the script tags exist there as well.

I don't think we can know if this works for tracking until we get verification from Jeroen (which might have to be after the non-preview site is built).

[machow]

Alright, let's just let this thing fly and see what happens!