feat: add contentful provider

[ykzts]

Resolve #330

It uses Contentful's Images API to transform images.

[pi0]

Thanks!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.90%. Comparing base (026be95) to head (f0b1154).
⚠️ Report is 948 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #398      +/-   ##
==========================================
+ Coverage   59.32%   59.90%   +0.58%     
==========================================
  Files          27       28       +1     
  Lines         622      631       +9     
  Branches      196      189       -7     
==========================================
+ Hits          369      378       +9     
  Misses        253      253              

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