feat: Add ClientID to Installation

[joshlarsen]

This PR adds ClientID to the Installation type.

Last year, GitHub added support for using the app ClientID to simplify the installation token flow. More detail in this blog post.

The test cases that involve Installation are also updated.

[gmlewis]

Thank you, @joshlarsen!
LGTM.

Please note that I still don't have write access to this repo, but figure I might as well attempt to catch up on my code reviews (which I usually allow the linter to process first... ah, well).

NOTE TO SELF: Rename "add" => "Add" for PR title consistency in this repo.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.12%. Comparing base (eef4b66) to head (b3b4d11).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #3712 +/- ##
=======================================
Coverage 91.12% 91.12% =======================================
Files 187 187 Lines 16640 16640 =======================================
Hits 15164 15164 Misses 1291 1291 Partials 185 185 

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[gmlewis]

@joshlarsen - I apologize, but could you please re-run step4 to update the auto-generated files and push the changes to this PR? Thank you!

[gmlewis]

Thank you, @joshlarsen!
LGTM.
Merging.