Implement organization of home page banners in Wagtail

[dorothyyeager]

As those of us who use Wagtail frequently know, too many banners has made the home view of Wagtail really cluttered. In https://github.com/fecgov/fec-cms/issues/1737, we figured out a way to organize the banners in their own section (as child pages of a draft page) and tested this out successfully in feature.

This issue is to implement the new system of organizing the banners in prod, so that we can easily find and access them when needed but they won't clutter up the home page. We're planning to do this after 5/25 when the important internet communications rulemaking banner is set to expire.

Completion criteria

• [ ] Set up draft page in Wagtail called "Banners"
• [ ] Move each banner to being a child page of the new "Banners" draft page.

[dorothyyeager]

Closing this issue in favor of #2004 which tackles the same thing and incorporates archiving old banners.