Fix Nova scp failures on Debian Bookworm

The addition of an instance resize operation [1] to CI testing is
triggering a failure in kolla-ansible-debian-ovn jobs, which are using a
nodeset with multiple nodes:

    oslo_concurrency.processutils.ProcessExecutionError: Unexpected error while running command.
    Command: scp -r /var/lib/nova/instances/8ca2c7e8-acae-404c-af7d-6cac38e354b8_resize/disk 192.0.2.2:/var/lib/nova/instances/8ca2c7e8-acae-404c-af7d-6cac38e354b8/disk
    Exit code: 255
    Stdout: ''
    Stderr: "Warning: Permanently added '[192.0.2.2]:8022' (ED25519) to the list of known hosts.\r\nsubsystem request failed on channel 0\r\nscp: Connection closed\r\n"

This is not seen on Ubuntu Jammy, which uses OpenSSH 8.9, while Debian
Bookworm uses OpenSSH 9.2. This is likely related to this change in
OpenSSH 9.0 [2]:

    This release switches scp(1) from using the legacy scp/rcp protocol
    to using the SFTP protocol by default.

Configure sftp subsystem like on RHEL9 derivatives. Even though it is
not yet required for Ubuntu, we also configure it so we are ready for
the Noble release.

[1] https://review.opendev.org/c/openstack/kolla-ansible/+/904249
[2] https://www.openssh.com/txt/release-9.0

Closes-Bug: #2048700
Change-Id: I9f1129136d7664d5cc3b57ae5f7e8d05c499a2a5

ansible/roles/nova-cell/templates/sshd_config.j2

@@ -8,4 +8,6 @@ SyslogFacility AUTHPRIV
 UsePAM yes
 {% if kolla_base_distro in ["centos", "rocky"] %}
 Subsystem       sftp    /usr/libexec/openssh/sftp-server
+{% elif kolla_base_distro in ["debian", "ubuntu"] %}
+Subsystem       sftp    /usr/lib/openssh/sftp-server
 {% endif %}

releasenotes/notes/bug-2048700-98eb939b72079173.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Fixes Nova operations using the ``scp`` command, such as cold migration or
+    resize, on Debian Bookworm. `LP#2048700
+    <https://bugs.launchpad.net/kolla-ansible/+bug/2048700>`__