github: migrate to new-style issue templates

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,8 @@
+blank_issues_enabled: false
+contact_links:
+#  - name: Electrum Security Policy
+#    url: https://github.com/spesmilo/electrum/blob/master/SECURITY.md
+#    about: View security policy
+  - name: Community Forum
+    url: https://bitcointalk.org/index.php?board=98.0
+    about: Ask non-development-related questions here