Replace use of serial with run_once

run_once on first node when database config enabled (so the first
node creates the tables), then wakeup all other nodes

roles/keycloak/tasks/start_keycloak.yml

@@ -0,0 +1,15 @@
+---
+- name: start keycloak
+  ansible.builtin.systemd:
+    name: keycloak
+    enabled: yes
+    state: started
+  become: yes
+
+- name: "Wait until Keycloak becomes active {{ keycloak.health_url }}"
+  ansible.builtin.uri:
+    url: "{{ keycloak.health_url }}"
+  register: keycloak_status
+  until: keycloak_status.status == 200
+  retries: 25
+  delay: 10