fix: update nova-compute notification config for telemetry meters

[munirsidd]

Change notification_format from versioned to both so that Ceilometer receives unversioned notifications on the notifications topic and Watcher receives versioned ones on the versioned_notifications topic [0][1]. Ceilometer already subscribes to both topics [2]. Add notify_on_state_change = vm_and_task_state to enable instance lifecycle notifications like compute.instance.booting.time.

[0] - https://docs.openstack.org/watcher/2026.1/configuration/configuring.html#configure-nova-notifications
[1] - https://docs.openstack.org/nova/2026.1/configuration/config.html#notifications.notification_format
[2] - https://opendev.org/openstack/sunbeam-charms/commit/15739a4dbf4245234c2a6348c14654f9c2980156

Partial-bug: #2162762

QA steps

1. Deploy sunbeam and enable telemetry

sunbeam enable telemetry

2. Build and install the openstack-hypervisor snap with this branch
3. Verify nova-compute config

grep -A5 oslo_messaging_notifications /var/snap/openstack-hypervisor/common/etc/nova/nova.conf
# [oslo_messaging_notifications]
# driver = messagingv2
#
# [notifications]
# notify_on_state_change = vm_and_task_state
# notification_format = unversioned

4. Launch an instance and verify compute.instance.booting.time metric

openstack server create --flavor m1.small --image ubuntu --network demo-network test-vm
openstack metric resource show <instance-id>
# Should include compute.instance.booting.time (missing without this fix)

5. Enable Watcher and verify it receives versioned notifications

Links

Jira card: OPEN-4670

[hemanthnakkina]

For Gazpacho I would like to leave the notification_format to versioned as all the measurements coming from notifications are already provided by pollster [1].

When you backport this for 2025.1 and 2024.1 notification_format=both is desired

[1] https://docs.openstack.org/ceilometer/latest/admin/telemetry-measurements.html#openstack-compute