Update new issue page on GitHub (#20736)

Move security vulnerability link into the config
Add questions/support link
Remove link to open a blank issue

.github/ISSUE_TEMPLATE/config.ylm

@@ -0,0 +1,8 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Report a security vulnerability
+    url: https://github.com/vector-im/element-web/security/policy
+    about: Please review our security policy for more details
+  - name: Questions & support
+    url: https://matrix.to/#/#element-web:matrix.org
+    about: Please ask and answer questions here.