Update custom TinkerbellTemplateConfig to use new static IPAM logic (#10338)

The custom template in TestTinkerbellCustomTemplateRefSimpleFlow was using
the deprecated STATIC_NETPLAN environment variable approach which was
removed in PR #10163. That PR changed the templating logic to directly
configure IPAM using netplan or NetworkManager by referencing the Hardware
object's network metadata.

This commit updates the custom template to:
- Remove STATIC_NETPLAN environment variable
- Add CONTENTS with Go template expressions that access network details
  directly from .Hardware.Interfaces[0].DHCP fields
- Support both VLAN and non-VLAN configurations using conditional logic
- Use netmaskToCIDR template function for proper CIDR notation
- Maintain the custom cexec action for test validation

The updated template now follows the same pattern as the default template
generation in NewDefaultTinkerbellTemplateConfigCreate, specifically
mirroring the withNetplanAction() function for Ubuntu OS family.

Ref: #10163

Author: rahulbabu95

test/framework/testdata/tinkerbell/custom_config.yaml

@@ -17,13 +17,50 @@ spec:
         name: stream image to disk
         timeout: 600
       - environment:
+          CONTENTS: |
+            {{ if (index .Hardware.Interfaces 0).DHCP.VLANID }}network:
+                version: 2
+                renderer: networkd
+                ethernets:
+                    mainif:
+                        match:
+                            macaddress: {{ (index .Hardware.Interfaces 0).DHCP.MAC }}
+                        set-name: mainif
+
+                vlans:
+                    vlan{{ (index .Hardware.Interfaces 0).DHCP.VLANID }}:
+                        id: {{ (index .Hardware.Interfaces 0).DHCP.VLANID }}
+                        link: mainif
+                        addresses:
+                        - {{ (index .Hardware.Interfaces 0).DHCP.IP.Address }}/{{ netmaskToCIDR (index .Hardware.Interfaces 0).DHCP.IP.Netmask }}
+                        nameservers:
+                            addresses: [{{ range $i, $ns := (index .Hardware.Interfaces 0).DHCP.NameServers }}{{if $i}}, {{end}}{{$ns}}{{end}}]
+                        {{- if (index .Hardware.Interfaces 0).DHCP.IP.Gateway }}
+                        routes:
+                            - to: default
+                              via: {{ (index .Hardware.Interfaces 0).DHCP.IP.Gateway }}
+                        {{- end }}
+            {{ else }}network:
+                version: 2
+                renderer: networkd
+                ethernets:
+                    id0:
+                        match:
+                            macaddress: {{ (index .Hardware.Interfaces 0).DHCP.MAC }}
+                        addresses:
+                            - {{ (index .Hardware.Interfaces 0).DHCP.IP.Address }}/{{ netmaskToCIDR (index .Hardware.Interfaces 0).DHCP.IP.Netmask }}
+                        nameservers:
+                            addresses: [{{ range $i, $ns := (index .Hardware.Interfaces 0).DHCP.NameServers }}{{if $i}}, {{end}}{{$ns}}{{end}}]
+                        routes:
+                            - to: default
+                              via: {{ (index .Hardware.Interfaces 0).DHCP.IP.Gateway }}
+            {{ end }}
           DEST_DISK: '{{ formatPartition ( index .Hardware.Disks 0 ) 2 }}'
           DEST_PATH: /etc/netplan/config.yaml
           DIRMODE: "0755"
           FS_TYPE: ext4
           GID: "0"
           MODE: "0644"
-          STATIC_NETPLAN: "true"
           UID: "0"
         image: 127.0.0.1/embedded/writefile
         name: write netplan config
@@ -54,11 +91,11 @@ spec:
           CONTENTS: |
             datasource:
               Ec2:
-                metadata_urls: [http://__TINKERBELL_LOCAL_IP__:50061,http://__TINKERBELL_LB_IP__:50061]
+                metadata_urls: [http://__TINKERBELL_LOCAL_IP__:50061, http://__TINKERBELL_LB_IP__:50061]
                 strict_id: false
             manage_etc_hosts: localhost
             warnings:
-              dsid_missing_source: off            
+              dsid_missing_source: off
           DEST_DISK: '{{ formatPartition ( index .Hardware.Disks 0 ) 2 }}'
           DEST_PATH: /etc/cloud/cloud.cfg.d/10_tinkerbell.cfg
           DIRMODE: "0700"
@@ -70,8 +107,7 @@ spec:
         name: add cloud-init config
         timeout: 90
       - environment:
-          CONTENTS: |
-                        datasource: Ec2
+          CONTENTS: "datasource: Ec2\n"
           DEST_DISK: '{{ formatPartition ( index .Hardware.Disks 0 ) 2 }}'
           DEST_PATH: /etc/cloud/ds-identify.cfg
           DIRMODE: "0700"