Add Giving Tuesday fundraising banner (Fixes #15527)

[alexgibson]

One-line summary

Adds home page fundraising banner experiment for Giving Tuesday.

Issue / Bugzilla link

#15527

Testing

Disable switch M24_WEBSITE_REFRESH

• http://localhost:8000/en-US/?v=a
• http://localhost:8000/en-US/?v=b
• http://localhost:8000/en-US/?v=c
• http://localhost:8000/de/?v=a
• http://localhost:8000/de/?v=b
• http://localhost:8000/de/?v=c
• http://localhost:8000/fr/?v=a
• http://localhost:8000/fr/?v=b
• http://localhost:8000/fr/?v=c

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.97%. Comparing base (2a4b476) to head (abc4cff).
Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15534      +/-   ##
==========================================
+ Coverage   78.95%   78.97%   +0.01%     
==========================================
  Files         158      158              
  Lines        8293     8298       +5     
==========================================
+ Hits         6548     6553       +5     
  Misses       1745     1745              

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[craigcook]

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