unable to provide autoinstall user-data to jammy-server-live-amd64.iso daily images with cloud-init 23.3.1

[Chad Smith]

During manual SRU verification of cloud-init 23.3.1 from jammy-proposed subiquity is unable to read cloud-init user-data containing autoinstall directives due to a traceback while trying to invoke stages.Init() prior to reading cloud-init combined user-data.

### From /var/log/installer/subiquity-server-debug.log
2023-10-03 17:00:49,502 INFO subiquity:163 Starting Subiquity server revision 5097 of snap /snap/subiquity/5097
...
2023-10-03 17:00:53,165 WARNING cloudinit.sources:1727 Failed loading pickled blob from /var/lib/cloud/instance/obj.pkl
2023-10-03 17:00:53,166 DEBUG cloudinit.sources:1736 Failed loading pickled blob from /var/lib/cloud/instance/obj.pkl
Traceback (most recent call last):
  File "/snap/subiquity/5097/usr/lib/python3/dist-packages/cloudinit/sources/__init__.py", line 1170, in pkl_load
    return pickle.loads(pickle_contents)
AttributeError: Can't get attribute 'Udhcpc' on <module 'cloudinit.net.dhcp' from '/snap/subiquity/5097/usr/lib/python3/dist-packages/cloudinit/net/dhcp.py'>

This traceback is due to unpickling errors due to an older version of cloud-init (23.2.2) installed in the snap being unable to unpickle the cached datasource written by the host version of cloud-init (23.3.1) at /var/lib/cloud/isntance/obj.pkl.

Because the subiquity snap updates cloud-init at a different pace than SRU's of cloud-init into jammy-updates, this issue will show up anytime cloud-init SRU's an update to classes or attributes related to the cached datasource object.

To avoid this unpickling incompatibility, subiquity already landed an upstream fix[1] to avoid using stages.Init() in favor of reading cloud-init's processed config artifact at /run/cloud-init/combined-cloud-config.json to get any `autoinstall` configuration.

This upstream release is not yet in the stable version of the subiquity snap #5097. And a release is expected in a couple of weeks that will contain this fix.

### References:
1: upstream fix to prefer /run/cloud-init/combined-cloud-config.json over stages.Init()
    https://github.com/canonical/subiquity/commit/751119866

### Reproducer steps:
## to be updated

wget https://cdimage.ubuntu.com/ubuntu-server/jammy/daily-live/current/jammy-live-server-amd64.iso

pull-lp-debs cloud-init jammy-proposed
# inject cloud-init from jammy-proposed
cat > proposed-actions.yaml <<EOF
- name: setup-rootfs
- name: cp
  source: /home/csmith/src/subiquity/cloud-init_23.3.1-0ubuntu1~22.04.1_all.deb
  dest: rootfs/cloud-init_23.3.1-0ubuntu1~22.04.1_all.deb
- name: shell
EOF

git clone <email address hidden>:mwhudson/livefs-editor.git
sudo PYTHONPATH=./livefs-editor python3 -m livefs_edit ./ubuntu-22.04.3-live-server-amd64.iso ./proposed-jammy-server.iso --actions proposed-actions.yaml

# At the /tmp prompt
chroot rootfs
dpkg -i /cloud-init*deb
exit
exit

mkdir -p ~/cidata
cd ~/cidata
cat > user-data << 'EOF'
#cloud-config
autoinstall:
  version: 1
  identity:
    hostname: ubuntu-server
    password: "$6$exDY1mhS4KUYCE/2$zmn9ToZwTKLhCw.b4/b.ZRTIZM30JZ4QrOQ2aOXJ8yk96xpcCof0kxKwuX1kqLG/ygbJ1f8wxED22bTL4F46P0"
    username: ubuntu
EOF
touch meta-data
cloud-localds ~/seed.iso user-data meta-data
truncate -s 10G image.img

$ kvm -name ci-test-kvm-live-server-ephemeral-1 -m 3G -drive file=image.img,format=raw,if=virtio -net nic -D qemu.log -net user,hostfwd=tcp::2222-:22 -cdrom ./proposed-jammy-server.iso -drive file=~/seed.iso,format=raw,if=ide -kernel /tmp/tmp1gro8vnk/vmlinuz -initrd /tmp/tmp1gro8vnk/initrd -append console=ttyS0 autoinstall -nographic

[Dan Bungert (dbungert)]

I can confirm with Chad's steps that Subiquity will fail to see the autoinstall.
Some telltale symptoms of this are:
1. the Subiquity TUI is showing the first screen instead of carrying out the autoinstall steps
2. the following log statement in /var/log/installer/subiquity-server-debug.log
`load_autoinstall_config only_early True file None`
3. the specific error for this issue, also in subiquity-server-debug.log
`Failed loading pickled blob from /var/lib/cloud/instance/obj.pkl`

To apply the fix, for now please run
sudo snap refresh --beta subiquity

After the refresh is complete, the Subiquity TUI should change to show the progress of the autoinstall. Log statements for that will look like:
```
Loaded cloud config from /run/cloud-init/combined-cloud-config.json
autoinstall found in cloud-config
load_autoinstall_config only_early True file /autoinstall.yaml
```

I suggest not holding cloud-init SRU, as the fix for this issue will be released on or around October-12th.