[Admin] Add a feedback button

[elia]

Summary

The button point at https://solidus.io/feedback?category=solidus-admin which will redirect most likely to a GH discussion, but could take to a more structured form over time.

Checklist

Check out our PR guidelines for more details.

The following are mandatory for all PRs:

• I have written a thorough PR description.
• I have kept my commits small and atomic.
• I have used clear, explanatory commit messages.

The following are not always needed:

• 📖 I have updated the README to account for my changes.
• 📑 I have documented new code with YARD.
• 🛣️ I have opened a PR to update the guides.
• ✅ I have added automated tests to cover my changes.
• 📸 I have attached screenshots to demo visual changes.

[the-krg]

Looks great 🚀

[codecov]

Codecov Report

Merging #5316 (1a620a8) into nebulab/admin (e2732fa) will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           nebulab/admin    #5316   +/-   ##
==============================================
  Coverage          88.55%   88.55%           
==============================================
  Files                601      601           
  Lines              14592    14592           
==============================================
  Hits               12922    12922           
  Misses              1670     1670           

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more