fix(flagd): fix parameter name inconsistency with SDK version 0.8.1

[gruebel]

This PR

• with version 0.8.1 of the SDK the parameter names are now internally enforced to be flag_key for the resolve_...() methods

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.99%. Comparing base (678ebd0) to head (997ee9d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #232   +/-   ##
=======================================
  Coverage   93.99%   93.99%           
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  Files          18       18           
  Lines         983      983           
=======================================
  Hits          924      924           
  Misses         59       59           

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