Add a scoped newsletter API user for the scheduled campaign task

Token is generated once and kept in Secret listmonk-newsletter-api.
Tested: create, test-send and schedule work; subscribers/settings 403.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/render.yml

@@ -18,6 +18,7 @@
         listmonk_smtp_password: render-only
         listmonk_oidc_client_secret: render-only
         listmonk_api_token: render-only-api-token
+        listmonk_newsletter_api_token: render-only-newsletter-token
     - name: Output directory
       ansible.builtin.file:
         path: "{{ out }}"