plugin XEP-0277: user friendly ID: when publishing a blog post without `id` specified, instead of using uuid, a user friendly ID based on title or content is used. This allow to have better URLs in web frontend. There is a (very low) risk of name collision if several articles with the same title or content are published on the same pubsub node, user friendly ID can be deactivated by using `user_friendly_id=False` in blog data to avoid that.

this certificates are used to enable TLS during tests. Those must be the same as in
backend_e2e (they are generated there)