fix(xcat-server): add an identity section to the Ubuntu autoinstall config

The generated Subiquity autoinstall config defined no identity section. Newer
Subiquity treats a config without an identity as incomplete and stops at an
interactive "Continue with autoinstall?" confirmation, so the install never
proceeds unattended (the prompt's advice to add 'autoinstall' to the kernel
command line is a red herring -- it was already present). Provide an identity
with a password sourced from the cluster passwd table so the install runs
non-interactively.

Signed-off-by: Daniel Hilst <392820+dhilst@users.noreply.github.com>

xCAT-server/share/xcat/install/ubuntu/compute.subiquity.tmpl

@@ -12,6 +12,11 @@ autoinstall:
     allow-pw: true
     authorized-keys: []
     install-server: true
+  identity:
+    realname: 'xCAT Admin'
+    username: xcatadm
+    hostname: #HOSTNAME#
+    password: "#CRYPTORLOCKED:passwd:key=system,username=root:password#"
 #UBUNTU_SUBIQUITY_APT_CONFIG#
   kernel:
     package: linux-generic