fix: Add prettier as a runtime dependency for snaps-webpack-plugin

[FrederikBolding]

Our Webpack plugin uses Prettier at runtime but does not specify it as a dependency. This breaks in repositories that do not have the expected version of Prettier already in the dependency tree.

[cryptodev-2s]

LGTM!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.28%. Comparing base (1382bf5) to head (08bd9cc).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3615   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files         417      417           
  Lines       11772    11772           
  Branches     1832     1832           
=======================================
  Hits        11570    11570           
  Misses        202      202           

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