add Copilot issue template (microsoft#254954)

* add copilot bug template

* remove text about internal backlog or public vscode

Author: Yoyokrazy

.github/ISSUE_TEMPLATE/copilot_bug_report.md

@@ -0,0 +1,19 @@
+---
+name: Copilot Bug report
+about: Create a report to help us improve Copilot's chat interface in VS Code
+---
+
+<!-- Please search existing issues to avoid creating duplicates -->
+<!-- Please attach logs to help us diagnose your issue -->
+
+- Copilot Chat Extension Version:
+- VS Code Version:
+- OS Version:
+- Feature (e.g. agent/edit/ask mode):
+- Selected model (e.g. GPT 4.1, Claude 3.7 Sonnet):
+- Logs:
+
+Steps to Reproduce:
+
+1.
+2.