DOC: Add comprehensive .github/copilot-instructions.md for coding agent onboarding#247

Copilot wants to merge 2 commits intomainmicrosoft/mssql-python:mainfrom

copilot/fix-2e6a883f-1a4b-49f2-ab0d-163c81decf0emicrosoft/mssql-python:copilot/fix-2e6a883f-1a4b-49f2-ab0d-163c81decf0eCopy head branch name to clipboard