backport ESM fix for importlib error

[blackboxsw]

CPC is looking to sync changes to ESM images for importlib errors seen on Pro images.
Backport upstream fix a97e746 as a quilt patch to ensure both focal and bionic get the destination patch.

Proposed Commit Message

Separate commits

* releasing cloud-init version 23.1.2-0ubuntu0~18.04.1+esm2

* fix: import specific importlib.util avoiding traces in pro auto-attach
    
    Use direct submodule import of importlib.util to avoid AttributeError
    tracebacks from ua-auto-attach.service on GCE.
    
    Backport-of: a97e7466
    Fixes GH-6924

Additional Context

As this is an ESM fix, this release will be reviewed by security team to be included in ESM infra PPA instead of typical Ubuntiu SRU process.
This upstream fix will make it into LTS releases via typical SRU process.

Test Steps

quilt push -a  # patches apply

lxc launch ubuntu-minimal:bionic b-min
lxc exec b-min -- pro attach <YOUR_TOKEN>
lxc exec b-min -- apt install ubuntu-pro-client cloud-init
lxc file push cloudinit/importer.py b-min/usr/lib/python3/dist-packages/cloudinit/
lxc exec b-min -- python3 /usr/lib/ubuntu-advantage/auto_attach.py   # confirm no traceback
quilt pop -a    # patched removed without issue

PPA for testing https://launchpad.net/~chad.smith/+archive/ubuntu/esm-test-pro-importlib

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)
• git merge from command line after approval.

[blackboxsw]

Manual verifcation performed: SUCCESS

cat > ESM.yaml <<EOF
#cloud-config
ubuntu_advantage:
  token: MY_TOKEN
EOF

cat > ESM.list <<EOF
deb [ allow-insecure=yes ] https://ppa.launchpadcontent.net/chad.smith/esm-backport-testing/ubuntu bionic main
EOF

lxc launch ubuntu-minimal:bionic b-esm-verification -c user.user-data="$(cat ESM_VALIDATION.yaml)"
lxc exec b-esm-verification -- cloud-init stauts --wait --format=yaml
lxc exec b-esm-verification -- apt install ubuntu-pro-client cloud-init -y  # latest ESM-released content

lxc exec b-esm-verification -- python3 /usr/lib/ubuntu-advantage/auto_attach.py   # confirm error
...
  File "/usr/lib/python3/dist-packages/cloudinit/mergers/__init__.py", line 134, in construct
    m_name, [__name__], [MERGER_ATTR]
  File "/usr/lib/python3/dist-packages/cloudinit/importer.py", line 52, in find_module
    if not importlib.util.find_spec(full_path):
AttributeError: module 'importlib' has no attribute 'util'


# install -proposed package from PPA
lxc file push ESM.list b-esm-verification/etc/apt/sources.list.d/

lxc exec b-esm-verification -- apt update
lxc exec b-esm-verification -- apt install cloud-init=23.1.2-0ubuntu0~18.04.1+esm2 --allow-unauthenticated -y
lxc exec b-esm-verification -- python3 /usr/lib/ubuntu-advantage/auto_attach.py   # confirm NO error
...
["2026-07-22T22:18:27.745", "INFO", "ubuntupro.lib.auto_attach", "main", 68, "cloud-init userdata has ubuntu-advantage key.", {}]
["2026-07-22T22:18:27.746", "INFO", "ubuntupro.lib.auto_attach", "main", 70, "Skipping auto-attach and deferring to cloud-init to setup and configure auto-attach", {}]
...

[blackboxsw]

Bumping quilt patch to explicitly retain an import importlib for importlib.import_module calls.