feat: uniform system.content source schema across installers and repositories

roles/global_defaults/tasks/validation.yml

@@ -148,8 +148,8 @@
 - name: Validate RHEL ISO requirement
   ansible.builtin.assert:
     that:
-      - os != "rhel" or (rhel_iso is defined and (rhel_iso | string | length) > 0)
-    fail_msg: "rhel_iso is required when os=rhel."
+      - os != "rhel" or system_cfg.content.source == "mirror" or (rhel_iso is defined and (rhel_iso | string | length) > 0)
+    fail_msg: "rhel_iso is required when os=rhel unless content.source is mirror."
     quiet: true
 
 - name: Validate hypervisor-specific required fields