Fix RKE2 MetalLB L2Advertisement to honor custom lb_pool_name (#135)

The apply-manifests role rendered the IPAddressPool from a template using
lb_pool_name, but applied the L2Advertisement from a hardcoded remote file
where the pool name was baked in as 'first-pool'. Setting lb_pool_name to
anything else left the L2Advertisement pointing at a non-existent pool, so
MetalLB assigned LoadBalancer IPs but never advertised them (services got an
external IP but were unreachable).

Template the L2Advertisement locally from lb_pool_name, mirroring the
IPAddressPool pattern, so both manifests always reference the same pool.

Ansible/Playbooks/RKE2/roles/apply-manifests/templates/metallb-l2advertisement.j2

@@ -0,0 +1,8 @@
+apiVersion: metallb.io/v1beta1
+kind: L2Advertisement
+metadata:
+  name: example
+  namespace: metallb-system
+spec:
+  ipAddressPools:
+  - {{ lb_pool_name }}