Add alphanumeric param to AutolinkOptions

[douglascayers]

Summary

Resolves #2449

Changes

• Adds IsAlphanumeric param to AutolinkOptions and Autolink structs of github/repos_autolinks.go
• Adds unit and integration tests for creating and getting autolinks for a repo
• Updates the createRandomTestRepository function in test/integration/github_test.go to look up the owner to create the repo under if a name isn't specified explicitly. Checks GITHUB_OWNER env var else falls back to user the oauth token belongs to.
• Removes redundant env var check from init function of test/integration/github_test.go because those checks already occur in the test/integration/authorizations_test.go file as needed. This made it easier for me to run integrations tests without setting env vars that weren't needed.

Tests

• github/repos_autolinks_test.go
• test/integration/repos_test.go

Created an alphanumeric autolink

Created a numeric autolink

[codecov]

Codecov Report

Merging #2450 (7e9fa62) into master (af69917) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2450   +/-   ##
=======================================
  Coverage   98.03%   98.03%           
=======================================
  Files         122      122           
  Lines       10690    10690           
=======================================
  Hits        10480    10480           
  Misses        144      144           
  Partials       66       66           

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

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[gmlewis]

Thank you very much, @douglascayers !
Looks great to me.

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

[douglascayers]

Hi @alexal, as a contributor to the autolinks feature, I'd appreciate your review of my proposed changes. Thanks!

[raynigon]

LGTM

[gmlewis]

Thank you, @raynigon !
Merging.