add support for oslo-messaging-notifications in Heat charm

[Fulga Fabian]

Currently, the Heat charm does not have the oslo_messaging_notifications section added to its config, which is required for Fleio to function properly. Based on the documentation https://fleio.com/docs/2024.10/configuring/enable-openstack-notifications.html#keystone-notifications, in order to integrate Fleio with an OpenStack environment, the following configuration is needed in the Heat service:

[oslo_messaging_notifications]
driver = messagingv2

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/charm-heat/+/933589

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-heat/+/933589
Committed: https://opendev.org/openstack/charm-heat/commit/91aa6015c4e30ddf46ab9fead0b7aa6e1eed2828
Submitter: "Zuul (22348)"
Branch: master

commit 91aa6015c4e30ddf46ab9fead0b7aa6e1eed2828
Author: Fabian Fulga <email address hidden>
Date: Mon Oct 28 17:48:51 2024 +0200

    Add `oslo_messaging_notifications` configuration to Heat charm

    This change introduces the `[oslo_messaging_notifications]` configuration section in the Heat charm, enabling Fleio integration with OpenStack by setting up the necessary notification driver. Previously, this configuration was missing, which prevented Fleio from receiving required notifications from Heat.

    The following section is now included in the `heat.conf`:

    ```
    {% include "section-oslo-notifications" %}
    ```

    Closes-Bug: #2085784
    Change-Id: I49778d60a7623ebdaea37edeba731d65a3dad15e