Add ParentIssueURL field to Issue struct

[SP3269]

Fixes#3840

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.41%. Comparing base (ea7dd81) to head (b75cb82).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #3841 +/- ##
=======================================
Coverage 92.41% 92.41% =======================================
Files 197 197 Lines 14152 14152 =======================================
Hits 13079 13079 Misses 884 884 Partials 189 189 

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[gmlewis]

Thank you, @SP3269!
LGTM.
Merging.