add contact form and mailing

Co-authored-by: Constantin Simonis <constantin@simonis.lol>
Reviewed-on: http://git.simonis.lol/sites/abiball/pulls/6
Reviewed-by: Constantin Simonis <constantin@simonis.lol>
Co-authored-by: Jan-Marlon Leibl <jleibl@proton.me>
Co-committed-by: Jan-Marlon Leibl <jleibl@proton.me>

config/packages/csrf.yaml

@@ -0,0 +1,11 @@
+# Enable stateless CSRF protection for forms and logins/logouts
+framework:
+    form:
+        csrf_protection:
+            token_id: submit
+
+    csrf_protection:
+        stateless_token_ids:
+            - submit
+            - authenticate
+            - logout