github: Add issue templates

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: false
+contact_links:
+  - name: ":thinking: Question and Help"
+    url: https://github.com/strongswan/strongswan/discussions
+    about: This issue tracker is not for support questions. Please refer to the strongSwan community's help and discussion forum