[stable/2024.1] fix: correct keystone_domains reference from horizon (#1503)

This is an automated cherry-pick of #1182
/assign mnaser
diff --git a/roles/horizon/vars/main.yml b/roles/horizon/vars/main.yml
index 31ebb28..a5461ef 100644
--- a/roles/horizon/vars/main.yml
+++ b/roles/horizon/vars/main.yml
@@ -31,7 +31,7 @@
             sso:
               enabled: true
               initial_choice: "{{ (keystone_domains is defined) | ternary(keystone_domains[0].name, 'atmosphere') }}"
-            idp_mapping: "{{ keystone_domains | default([{'name': 'atmosphere', 'label': 'Atmosphere'}]) | vexxhost.atmosphere.keystone_domains_to_idp_mappings }}" # noqa: yaml[line-length]
+            idp_mapping: "{{ keystone_domains | default([{'name': (keystone_keycloak_realm | default('atmosphere')), 'label': (keystone_keycloak_realm_name | default('Atmosphere'))}]) | vexxhost.atmosphere.keystone_domains_to_idp_mappings }}" # noqa: yaml[line-length]
           raw:
             OPENSTACK_SSL_NO_VERIFY: "{{ ((cluster_issuer_type | default('self-signed')) == 'self-signed') | ternary('True', 'False') | string }}"
             WEBSSO_KEYSTONE_URL: https://{{ openstack_helm_endpoints['identity']['host_fqdn_override']['public']['host'] }}/v3