Implement accessibilty suggestions for Onboarding carousel

[schu96]

Closes #7848

Fix

Technical

Increases the text spacing between the header and subtitle text within the Onboarding carousel cards.

Changes the text color from grey hsl (330, 3%, 62%) to black hsl (0, 0%, 20%) to increase the contrast ratio

Testing

Navigate to localhost:8080 and use a web accessibility tool to verify that the contrast ratio should pass the WCAG 2.1 AA/AAA guidelines.

Screenshot

Before

After

Stakeholders

@mekarpeles

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 17.44%. Comparing base (3025f5d) to head (3905879).
Report is 72 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10235      +/-   ##
==========================================
- Coverage   17.44%   17.44%   -0.01%     
==========================================
  Files          89       89              
  Lines        4792     4793       +1     
  Branches      848      849       +1     
==========================================
  Hits          836      836              
  Misses       3436     3436              
- Partials      520      521       +1     

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[mekarpeles]

Thank you!