Refresh: homepage - hero, update to black with flag (Fix#15482)

[stephaniehobson]

One-line summary

Update homepage hero to most recent Figma.

Significant changes and points to review

• Make the homepage "hero" its own component, separate from about page
• HTML, CSS, and images to support the new "hero" on the homepage
• Add alt white and black colours

Issue / Bugzilla link

Fix #15482

Testing

http://localhost:8000/en-US/ with refresh switch on

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.71%. Comparing base (e4df84e) to head (b2fbb8d).
Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15508   +/-   ##
=======================================
  Coverage   78.71%   78.71%           
=======================================
  Files         156      156           
  Lines        8197     8197           
=======================================
  Hits         6452     6452           
  Misses       1745     1745           

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