Improve 3-debootstrap example for Debian 13+

Debian 13+ no longer include isc-dhcp-server (or any DHCP client it
seems) in their default minimal stack. This can cause cloud-init to fail
early and render newly provsiioned VMs unbootable. We add it to the
example here for posterity. We also explicitly add ifupdown, which
provides the legacy Debian networking subsystem.

Finally we modify the cloud-init to ensure it does not attempt to
overwrite the networking provided by the system, and reduce timeouts to
avoid excessive delays.

api-daemon/provisioner/examples/script/3-debootstrap.py

@@ -485,6 +485,8 @@ class VMBuilderScript(VMBuilder):
                 "acpid",
                 "acpi-support-base",
                 "wget",
+                "ifupdown",  # be explicit for Debian 13+
+                "isc-dhcp-server",  # required for cloud-init on Debian 13+ where this is no longer standard
             ]
 
         # We need to know our root disk for later GRUB-ing
@@ -585,13 +587,15 @@ After=multi-user.target
                 disable_root: true
                 
                 preserve_hostname: true
+
+                network:
+                  config: disabled
                 
                 datasource:
                   Ec2:
                     metadata_urls: ["http://169.254.169.254:80"]
-                    max_wait: 30
-                    timeout: 30
-                    apply_full_imds_network_config: true
+                    max_wait: 5
+                    timeout: 5
                 
                 cloud_init_modules:
                  - migrator