Add support for SAML SSO authorization APIs

[joaopenteado]

This PR adds support for both ListCredentialAuthorizations and RemoveCredentialAuthorization methods available for the GitHub Enterprise Cloud REST API for SAML SSO authorizations.

Listing and deleting credential authorizations is available to organizations with GitHub Enterprise Cloud.

[gmlewis]

Thank you, @joaopenteado !
Just a few tweaks, please, then we will be ready for a second LGTM+Approval from any other contributor to this repo before merging.

[codecov]

Codecov Report

Merging #2835 (529eb79) into master (b02bb75) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2835   +/-   ##
=======================================
  Coverage   98.06%   98.06%           
=======================================
  Files         137      138    +1     
  Lines       12291    12314   +23     
=======================================
+ Hits        12053    12076   +23     
  Misses        162      162           
  Partials       76       76           

Impacted Files	Coverage Δ
github/orgs_credential_authorizations.go	100.00% <100.00%> (ø)

[gmlewis]

Thank you, @joaopenteado !
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[joaopenteado]

Thank you for the fast review and comments as always, @gmlewis!
I just committed a improvement to the test for ListCredentialAuthorizations in order to match what was being done in other functions.

[gmlewis]

Awesome, @joaopenteado ! Thank you very much!
I was wondering why the coverage dropped, but it looks like you found it and fixed it!
🎉

[o-sama]

LGTM too :)

[gmlewis]

Thank you, @o-sama !
Merging.