Add signup button to feedback panel

[rfultz]

Summary

• Resolves Add usability testing sign up link/code to feedback box and update form #6497

Adding a new section to the Feedback panel

Required reviewers

• UX/design
• 1 front-end

Impacted areas of the application

The feedback panel on the homepage and site-wide

Screenshots

Related PRs

None

How to test

• Pull the branch
• npm i
• npm run build
• ./manage.py runserver
• At different widths, open the feedback box and click the signup form on
  • Homepage
  • Wagtail page
  • Data page

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.91%. Comparing base (e73dd1b) to head (6f38a4b).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #6548   +/-   ##
========================================
  Coverage    79.91%   79.91%           
========================================
  Files          235      235           
  Lines         5147     5147           
========================================
  Hits          4113     4113           
  Misses        1034     1034           

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