feat(Browse&Request): update decline modal UX and add decline reason …

[hkumar1-sonata]

…field

• Updated enrollment decline popup modal per Figma design
• Removed "send learner email notification" option
• Removed "disassociate learner from organization" option
• Added new Decline Reason text field (string, max 250 chars, optional)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.11%. Comparing base (d933fba) to head (7392ea1).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1728      +/-   ##
==========================================
- Coverage   87.11%   87.11%   -0.01%     
==========================================
  Files         781      781              
  Lines       17880    17878       -2     
  Branches     3746     3746              
==========================================
- Hits        15576    15574       -2     
  Misses       2229     2229              
  Partials       75       75              

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