Reno only - Check for available networks for a role

Since change: I07822ec0cba7eed352c0010eb893b5e5a522e95c
resources are no longer created for networks that are not
defined in roles data. While this is an improvement we
need to communicate this change.

There is tribal knowledge and documentation that failed
reflect the requirement to add networks to roles data
since the introduction of composable networks in Pike.

Prior to Pike adding a network to a role was achived by
overriding the resource_registry entry to not use the
noop.yaml fake port (fall back to ctlplane) template.
i.e to add External network to compute role the
following was commonly added to network-environment.yaml

  OS::TripleO::Compute::Ports::ExternalPort:
    ../network/ports/external.yaml

NOTE: Current OVN-DVR and ODL doc's downstream uses the
      resource_registry override, whitout also adding
      the network to roles data.

Related-Bug: #1800811
Change-Id: I6c03c7a2bd6f369bf35a9e479a97302c9a455197

releasenotes/notes/check-availble-network-in-role-7860d8d5cd1df4b0.yaml

@@ -0,0 +1,34 @@
+---
+upgrade:
+  - |
+    Deployers that used ``resource_registry`` override in their environment
+    to add networks to roles without also using a custom roles data file must
+    create a custom roles data file and add the additional network(s) and use
+    this when upgrading.
+
+    Previously it was possible to add additional networks to a role without
+    using a custom role by overriding the resource registry, for example::
+
+      OS::TripleO::Compute::Ports::ExternalPort: ../network/ports/external.yaml
+
+    .. Warning:: Since resources are no longer added to the plan unless the
+                 network is specified in the role, the ``resource_registry``
+                 override alone is no longer sufficient.
+critical:
+  - |
+    Networks not specified for roles in roles data (``roles_data.yaml``) no
+    longer have Heat resources created. It is now mandatory that custom roles
+    are used when non-default networks is used for a role.
+
+    Previously it was possible to add additional networks to a role without
+    using a custom role by overriding the resource registry, for example::
+
+      OS::TripleO::Compute::Ports::ExternalPort: ../network/ports/external.yaml
+
+    .. Note:: The ``resource_registry`` override was the only requirement prior
+              to the introduction of *Composable Networks* in the Pike release.
+
+              Since Pike a custom role would ideally be used when adding
+              networks to roles, but documentation and other guides may not
+              have been properly updated and only mention the
+              ``resource_registry`` override.