WT-303: New Mozilla ads pages

[lucianoratamero]

Summary

This PR adds the new pages for the Mozilla Ads section.
It contains:

• updates to the main and principles pages (WT-302);
• new design for the Why Mozilla page (WT-304);
• new design for the Contact Sales page (WT-305);
• new design for the Solutions page (WT-303).

Significant changes and points to review

Issue / Bugzilla link

https://mozilla-hub.atlassian.net/browse/WT-302
https://mozilla-hub.atlassian.net/browse/WT-303
https://mozilla-hub.atlassian.net/browse/WT-304
https://mozilla-hub.atlassian.net/browse/WT-305

Testing

I have the designs fully implemented on the remainder of the Ads pages. Some notes:

Please review for design as well, as all of the typography has been refactored to better align with the base styles, and there are a lot of new patterns here too.

https://www-demo1.allizom.org/en-US/advertising/
https://www-demo1.allizom.org/en-US/advertising/solutions/
https://www-demo1.allizom.org/en-US/advertising/why-mozilla/
https://www-demo1.allizom.org/en-US/advertising/principles/

[codecov]

Codecov Report

❌ Patch coverage is 45.45455% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.66%. Comparing base (a59a279) to head (ecc8f26).

Files with missing lines	Patch %	Lines
bedrock/mozorg/views.py	40.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16810      +/-   ##
==========================================
- Coverage   79.70%   79.66%   -0.05%     
==========================================
  Files         159      159              
  Lines        8534     8545      +11     
==========================================
+ Hits         6802     6807       +5     
- Misses       1732     1738       +6     

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