Adds explicit content-type in search function

[julcansado]

Regarding #29, explicitly tells the provider that the content-type is application/json in the search() function

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.77%. Comparing base (1d6519d) to head (6a7f562).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #30   +/-   ##
=======================================
  Coverage   75.77%   75.77%           
=======================================
  Files           9        9           
  Lines         322      322           
=======================================
  Hits          244      244           
  Misses         78       78           

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[Alexander-Barth]

Thanks a lot @julcansado !