Determine active_server once per cluster, not once for all

While `first_server.yml` would only be included for the 1st server of a cluster,
`run_once` for setting the `active_server` fact also meant this would only happen once
for all clusters instead of once per cluster.

Use a loop across the members of each cluster and a fact delegation instead, to set the
`active_server` fact instead on each cluster member to the `inventory_hostname` of the
server, for which `first_server.yml` was included.

Author: eliasp

tasks/first_server.yml

@@ -145,7 +145,9 @@
 - name: Set an Active Server variable
   ansible.builtin.set_fact:
     active_server: "{{ inventory_hostname }}"
-  run_once: true
+  delegate_to: "{{ item }}"
+  delegate_facts: true
+  loop: "{{ groups[rke2_cluster_group_name] }}"
 
 - name: Get all nodes
   ansible.builtin.shell: |