WT-827 Add alternative mobile text to carousel slides

[maribedran]

One-line summary

Add a new mobile headline field to Home Carousel slides with an alternative mobile text.

Issue / Bugzilla link

https://mozilla-hub.atlassian.net/browse/WT-827

Testing

Edit the homepage carousel and add mobile content to the slides

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.26%. Comparing base (ce81cd6) to head (c5d07a2).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1096   +/-   ##
=======================================
  Coverage   77.25%   77.26%           
=======================================
  Files         124      124           
  Lines        7620     7621    +1     
=======================================
+ Hits         5887     5888    +1     
  Misses       1733     1733           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.