Change MetalLB to one of addons (#6238)

This changes MetalLB contrib to one of addons for deploying MetalLB with
Kubernetes cluster deployment. By the default, Kubespray doesn't deploy
MetalLB addon.

roles/kubernetes-apps/metallb/templates/metallb-config.yml.j2

@@ -0,0 +1,25 @@
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  namespace: metallb-system
+  name: config
+data:
+  config: |
+    address-pools:
+    - name: loadbalanced
+      protocol: {{ metallb_protocol }}
+      addresses:
+{% for ip_range in metallb_ip_range %}
+      - {{ ip_range }}
+{% endfor %}
+{% if metallb_additional_address_pools is defined %}{% for pool in metallb_additional_address_pools %}
+    - name: {{ pool }}
+      protocol: {{ metallb_additional_address_pools[pool].protocol }}
+      addresses:
+{% for ip_range in metallb_additional_address_pools[pool].ip_range %}
+      - {{ ip_range }}
+{% endfor %}
+      auto-assign: {{ metallb_additional_address_pools[pool].auto_assign }}
+{% endfor %}
+{% endif %}