feat: Support getting an organization role

[felixlut]

Resolves #3282

It was only possible to list organization roles before, this makes it possible to get a specific one.

I might have went overboard with the test-cases (testing both a custom role and a built-in one). I haven't written mocks before, so I'm not sure what the best practices are here 😅

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.95%. Comparing base (2b8c7fa) to head (68caaad).
Report is 119 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3285      +/-   ##
==========================================
- Coverage   97.72%   92.95%   -4.77%     
==========================================
  Files         153      171      +18     
  Lines       13390    11679    -1711     
==========================================
- Hits        13085    10856    -2229     
- Misses        215      729     +514     
- Partials       90       94       +4     

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[gmlewis]

Thank you, @felixlut !
LGTM.

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

[tomfeigin]

LGTM

[gmlewis]

Thank you, @tomfeigin !
Merging.