feat: Openfeature SDK spec 0.8 support

[thomaspoignant]

Description

A new version of the Openfeature SDK is ongoing with the support of the v0.8.0 spec.
A pull request is open for this one.

This PR is to be compatible with the latest version of the SDK.

Warning

Before merging this version we need to change the dependency to link to the new version of the SDK (when it is released) and not to the branch as it is now.

Closes issue(s)

Resolve #12

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have followed the contributing guide

[codecov]

Codecov Report

Attention: Patch coverage is 70.21277% with 14 lines in your changes missing coverage. Please review.

Project coverage is 85.91%. Comparing base (91a9a90) to head (da09493).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/OFREP/ofrep.swift	70.27%	11 Missing ⚠️
Sources/GOFeatureFlag/provider.swift	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #15      +/-   ##
==========================================
- Coverage   86.36%   85.91%   -0.45%     
==========================================
  Files          23       23              
  Lines        1144     1143       -1     
==========================================
- Hits          988      982       -6     
- Misses        156      161       +5     

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