Ubuntu: pin base container image

Previously when building Kolla container images for Ubuntu it was common
to get a dependency error during apt package installation, such as:

    The following packages have unmet dependencies:
     libc6-dev : Depends: libc6 (= 2.35-0ubuntu3.1) but 2.35-0ubuntu3.4 is to be installed

This is caused by the packages in the Ubuntu base image being newer than
those in the release train repository snapshot.

This change fixes the issue by pinning the Ubuntu base image to a
specific tag to ensure that its packages are older than the release
train repository snapshots.

This tag should be updated with the Ubuntu repository versions to the
most recent tag that precedes the repository versions.

Available tags shown here: https://hub.docker.com/_/ubuntu/tags?page=1&name=jammy

etc/kayobe/kolla/kolla-build.conf

@@ -1,2 +1,10 @@
 [DEFAULT]
 build_args = {{ kolla_build_args.items() | map('join', ':') | join(',') }}
+{% if kolla_base_distro == 'ubuntu' %}
+# Pin to a specific Ubuntu Jammy image to ensure that its packages are older
+# than the release train repository snapshots. This tag should be updated with
+# the Ubuntu repository versions to the most recent tag that precedes the
+# repository versions.
+# Tags: https://hub.docker.com/_/ubuntu/tags?page=1&name=jammy
+base_tag = jammy-20230916
+{% endif %}