Add support for the secret scanning API

[wtfiscrq]

This PR adds support for the Secret Scanning API. Includes all endpoints and structures listed on the API documentation.

Closes #2278

[gmlewis]

Thank you, @crqra !

[codecov]

Codecov Report

Merging #2281 (000bc40) into master (e1c28bc) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2281      +/-   ##
==========================================
+ Coverage   97.81%   97.83%   +0.01%     
==========================================
  Files         114      115       +1     
  Lines       10266    10357      +91     
==========================================
+ Hits        10042    10133      +91     
  Misses        156      156              
  Partials       68       68              

Impacted Files	Coverage Δ
github/github.go	97.63% <100.00%> (+<0.01%)	⬆️
github/secret_scanning.go	100.00% <100.00%> (ø)
github/event_types.go	100.00% <0.00%> (ø)

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[wtfiscrq]

Thanks for the feedback @gmlewis! I've updated the PR with your suggestions, LMK if it looks good 😄

[gmlewis]

Thank you, @crqra !
LGTM.
Awaiting second LGTM/Approval before merging.

[gmlewis]

@Parker77 - do you have time to review this PR?

[Parker77]

LGTM.

[gmlewis]

Thank you, @Parker77 !
Merging.