feat: Add graphQL API support

[Abhi347]

WIP

fixes #87

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 85.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 77.43%. Comparing base (abc0285) to head (039457d).

:exclamation: Current head 039457d differs from pull request most recent head d86b494

Please upload reports for the commit d86b494 to get more accurate results.

Files	Patch %	Lines
...va/com/spotify/github/v3/clients/GitHubClient.java	85.00%	3 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #183      +/-   ##
============================================
+ Coverage     76.18%   77.43%   +1.25%     
- Complexity      313      314       +1     
============================================
  Files            44       44              
  Lines          1058     1059       +1     
  Branches         44       44              
============================================
+ Hits            806      820      +14     
+ Misses          227      214      -13     
  Partials         25       25              

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