fix(metallb): guard cilium_bgp when undefined; clarify apiserver_endpoint docs (#683)

* fix(metallb): guard cilium_bgp variable before evaluating

- The 'Deploy metallb manifest' and 'Deploy metallb pool' conditionals evaluate
  'not cilium_bgp' directly, which raises an undefined-variable error when the
  k3s_server role runs without cilium_bgp in scope and no Cilium variables are set
- Guard with 'cilium_bgp is not defined' so the condition resolves cleanly when
  Cilium BGP is not configured
- Fixes #644

* docs(apiserver): clarify apiserver_endpoint must be a free routable IP

- Note that apiserver_endpoint must be an unassigned, routable IP on the
  network and that it is exposed by kube-vip / MetalLB
- Fixes #678

* fix(molecule): wait for MetalLB resources before asserting images

- The MetalLB image-tag assertion crashed with 'list object has no element 0'
  when the controller Deployment was not yet observable at verify time
- Retry the MetalLB controller/speaker lookup until the resources appear
- Fail with a clear message if MetalLB is genuinely absent

molecule/resources/verify_from_outside/tasks/test/verify-components.yml

@@ -219,12 +219,26 @@
             namespace: metallb-system
             kubeconfig: "{{ kubecfg_path }}"
           register: metallb_info
+          until: metallb_info.resources | length > 0
+          retries: 15
+          delay: 10
           loop:
             - { kind: Deployment, name: controller }
             - { kind: DaemonSet, name: speaker }
           loop_control:
             label: "{{ item.kind }}/{{ item.name }}"
 
+        - name: Fail with a clear message if MetalLB resources are missing
+          ansible.builtin.fail:
+            msg: >-
+              Did not find {{ item.kind | lower }} {{ item.name }} in
+              metallb-system. Expected MetalLB to be deployed in this
+              scenario (verify_lb: {{ verify_lb }}).
+          when: item.resources | length == 0
+          loop: "{{ metallb_info.results }}"
+          loop_control:
+            label: "{{ item.item.kind }}/{{ item.item.name }}"
+
         - name: Assert MetalLB controller and speaker use the expected image tags
           ansible.builtin.assert:
             that: