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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.78%. Comparing base (618d5c2) to head (a67f12c). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #15508 +/- ## ======================================= Coverage 78.78% 78.78% ======================================= Files 157 157 Lines 8257 8257 ======================================= Hits 6505 6505 Misses 1752 1752 ```

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