Add Dockerfile for neutron-ovn-agent

This patch adds support for the new OVN Neutron Agent [1]. This
new agent will include any needed OVN functionality not implemented
in ovn-controller. This agent will, in a future, include the
metadata service, superseding the OVN Metadata Agent.

[1]https://review.opendev.org/c/openstack/neutron-specs/+/868076

Related-Bug: #2000385
Related-Bug: #1998608
Change-Id: Ib15a89ce9ba7b1c5121a627da9d130dc5bf5a044

docker/neutron/neutron-ovn-agent/Dockerfile.j2

@@ -0,0 +1,18 @@
+FROM {{ namespace }}/{{ image_prefix }}neutron-base:{{ tag }}
+{% block labels %}
+LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
+{% endblock %}
+
+{% block neutron_ovn_agent_header %}{% endblock %}
+
+{% import "macros.j2" as macros with context %}
+
+{% set neutron_ovn_agent_packages = [
+] %}
+
+{{ macros.install_packages(neutron_ovn_agent_packages | customizable("packages")) }}
+
+{% block neutron_ovn_agent_footer %}{% endblock %}
+{% block footer %}{% endblock %}
+
+USER neutron

releasenotes/notes/neutron-ovn-agent-kolla-image-38ab7ef7203e8963.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    The OVN Neutron Agent container image (``neutron-ovn-agent``) has
+    been added.