Include fix for default(omit) placeholder leak in install-config template (PR #20)

Cherry-picked from fix-omit-leak-install-config branch to unblock CI.
Without this fix, openshift-install fails immediately with:
  "platform.openstack.controlPlanePort.fixedIPs[0].subnet.id:
   Invalid value: __omit_place_holder__...: invalid subnet ID"

The omit sentinel leaks because default(omit) only works in Ansible
module parameters, not in vars passed to ansible.builtin.template.
This fix uses empty defaults and truthiness checks instead.

OCPBUGS-95045

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: tusharjadhav3302

collection/stages/roles/install/tasks/install_config_generation/ipi_install_config.yml

@@ -45,9 +45,9 @@
     installcfg_api_vips: "{{ ocp_deployment_topology.primary_ip_protocol == 'ipv6' }}"
     installcfg_api_floating_ip: "{{ precreated_api_fip }}"
     installcfg_ingress_floating_ip: "{{ precreated_ingress_fip }}"
-    installcfg_machines_subnet: "{{ machines_subnet_id | default(omit) }}"
+    installcfg_machines_subnet: "{{ machines_subnet_id | default('') }}"
     installcfg_cluster_network: "{{ ocp_deployment_topology[ocp_deployment_topology.primary_ip_protocol].cluster_network }}"
     installcfg_service_network: "{{ ocp_deployment_topology[ocp_deployment_topology.primary_ip_protocol].service_network }}"
     installcfg_default_machine_platform: "{{ ocp_deployment_topology.defaultMachinePlatform | default({}) }}"
     installcfg_cluster_os_image_properties: "{{ ocp_deployment_topology.platform.openstack.clusterOSImageProperties | default({}) }}"
-    installcfg_additional_trust_bundle: "{{ _cacert_content.stdout_lines | default(omit) }}"
+    installcfg_additional_trust_bundle: "{{ _cacert_content.stdout_lines | default([]) }}"

collection/stages/roles/install/templates/install-config-ipi.yaml.j2

@@ -45,7 +45,7 @@ platform:
       {{ key }}: {{ value }}
       {%- endfor +%}
     {%- endif +%}
-    {%- if installcfg_machines_subnet is defined +%}
+    {%- if installcfg_machines_subnet +%}
     machinesSubnet: {{ installcfg_machines_subnet }}
     {%- endif +%}
     {%- if installcfg_api_vips +%}
@@ -64,15 +64,15 @@ platform:
     externalNetwork:  "{{ installcfg_external_network }}"
     apiFloatingIP:     "{{ installcfg_api_floating_ip }}"
     ingressFloatingIP: "{{ installcfg_ingress_floating_ip }}"
-    {%- if installcfg_machines_subnet is not defined +%}
+    {%- if not installcfg_machines_subnet +%}
     externalDNS: {{ installcfg_dns_servers }}
     {%- endif +%}
     {%- endif +%}
 pullSecret: |
   {{ ocp_pull_secret }}
 sshKey: |
   {{ ocp_public_key }}
-{%- if installcfg_additional_trust_bundle is defined +%}
+{%- if installcfg_additional_trust_bundle +%}
 additionalTrustBundle: |
 {% for line in installcfg_additional_trust_bundle %}
   {{ line }}