Add flashcard component

[trenaryja]

This PR adds the Flashcard component to the Design System, which show's the backside content when clicked (after a flipping animation)

Example:

Screen.Recording.2023-08-16.at.4.43.49.PM.mov

[codecov]

Codecov Report

Patch coverage: 97.14% and project coverage change: +0.01% 🎉

Comparison is base (29bd844) 95.74% compared to head (97a6e44) 95.76%.
Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1382      +/-   ##
==========================================
+ Coverage   95.74%   95.76%   +0.01%     
==========================================
  Files         203      205       +2     
  Lines        2422     2457      +35     
  Branches      462      478      +16     
==========================================
+ Hits         2319     2353      +34     
- Misses         49       50       +1     
  Partials       54       54              

Files Changed	Coverage Δ
packages/core/src/theme/theme.ts	100.00% <ø> (ø)
packages/core/src/Flashcard/Flashcard.tsx	97.05% <97.05%> (ø)
packages/core/src/Flashcard/index.ts	100.00% <100.00%> (ø)

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