Add contribution option to bug report template

Added a contribution checkbox to the bug report template.

Author: w-ahmad

.github/ISSUE_TEMPLATE/bug_report.md

@@ -22,3 +22,6 @@ If applicable, add screenshots to help explain your problem.
 ### Environment:
  - Package Version:
  - WinAppSDK Version:
+
+### Contribution:
+- [ ] I am willing to submit a PR to fix this issue