Allow to set dnsmasq configuration options

This is useful to work around
https://bugs.launchpad.net/ubuntu/+source/dnsmasq/+bug/1974230 by setting
"no-negcache" into neutron_dhcp_config_list.

Change-Id: I1a0c1b5a125c72635efc89c9763aa41bfb503a3f

defaults/main.yml

@@ -121,6 +121,11 @@ neutron_dns_domain: "{{ dhcp_domain | default('openstacklocal.') }}"
 #  dhcp-option-force: "26,1500"
 neutron_dhcp_config: {}
 
+# Dnsmasq has furthermore some options in its configuration that are not
+# key/value pairs but just options. A deployer can configure those with this
+# list:
+neutron_dhcp_config_list: []
+
 # Disable dnsmasq to resolve DNS via local resolv.conf.
 # When dnsmasq_dns_servers are not set,
 # and neutron_dnsmasq_noresolv is set to True, dnsmasq will reply with

releasenotes/notes/neutron-dhcp-config-list-3e9354e5da138b53.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    You can configure options for dnsmasq by adding those to the newly
+    introduced ``neutron_dhcp_config_list`` list. This helps to configure e.g.
+    ``no-negcache`` to get around
+    https://bugs.launchpad.net/ubuntu/+source/dnsmasq/+bug/1974230.

templates/dnsmasq-neutron.conf.j2

@@ -3,6 +3,9 @@
 {% for key, value in neutron_dhcp_config.items() %}
 {{ key }}={{ value }}
 {% endfor %}
+{% for option in neutron_dhcp_config_list %}
+{{ option }}
+{% endfor %}
 user={{ neutron_system_user_name }}
 {% if neutron_dnsmasq_noresolv %}
 no-resolv