Default CephDashboardNetwork to storage_dashboard

The default CephDashboardNetwork in ServiceNetMap was
'ctlplane'. Change this to default to storage_dashboard
with a fallback to 'ctlplane'.

This will allow us to remove the hard-coded conditionals
on 'StorageDashboard' network name in tripleo_hiera_data.

Conflicts:
  overcloud-resource-registry-puppet.j2.yaml

Related-Bug: #1946239
Change-Id: I9a62b2cf24b2dd020de74e18af8c7bc0535d12d9
(cherry picked from commit 28161b5868)
(cherry picked from commit 5d4785bd61)

network/service_net_map.j2.yaml

@@ -77,7 +77,7 @@ parameters:
       MysqlNetwork: {{ _service_nets.get('internal_api', 'ctlplane') }}
       SnmpdNetwork: ctlplane
       CephClusterNetwork: {{ _service_nets.get('storage_mgmt', 'ctlplane') }}
-      CephDashboardNetwork: ctlplane
+      CephDashboardNetwork: {{ _service_nets.get('storage_dashboard', 'ctlplane') }}
       CephGrafanaNetwork: {{ _service_nets.get('storage', 'ctlplane') }}
       CephMonNetwork: {{ _service_nets.get('storage', 'ctlplane') }}
       CephRgwNetwork: {{ _service_nets.get('storage', 'ctlplane') }}