Make "obtain certificates" tasks have unique names

We always skip at least one of these tasks, depending on which
SSL retrieval method is enabled, so it could have been confusing why.

roles/matrix-server/tasks/setup/ssl/setup_ssl_lets_encrypt.yml

@@ -25,7 +25,7 @@
     name: "{{ matrix_ssl_lets_encrypt_certbot_docker_image }}"
   when: "matrix_ssl_retrieval_method == 'lets-encrypt'"
 
-- name: Obtain certificates
+- name: Obtain Let's Encrypt certificates
   include_tasks: "tasks/setup/ssl/setup_ssl_lets_encrypt_obtain_for_domain.yml"
   with_items: "{{ domains_requiring_certificates }}"
   loop_control: