Handle the hardcoded configuration values

This patch allows to customize the hardcoded configuration values,
as well as introduce new configuration options for neutron services
by configmap template with the specified section:

    neutron:
      server:
        configmap:
          neutron_server:
            quotas:
              quota_network: 20
              quota_subnet: 10
              quota_port: 100
          gateway:
            metadata_agent:
              DEFAULT:
                metadata_workers: 10
                debug: True
              agent:
                report_interval: 30
            l3_agent:
              DEFAULT:
                agent_mode : dvr
              agent:
                report_interval: 40
            dhpc_agent:
              DEFAULT:
                ovs_vsctl_timeout: 12
                resync_interval: 60
              agent:
                report_interval: 60

Change-Id: If4ae2530a0d0ebe71d0689fc2a5ffb121f49acbd
Related-Prod: PROD-29040
diff --git a/README.rst b/README.rst
index 8986c63..eb45711 100644
--- a/README.rst
+++ b/README.rst
@@ -1638,6 +1638,46 @@
           workers: 64
           logto: /var/log/neutron/neutron-server.log
 
+Setup hardcoded configuration values
+------------------------------------
+
+.. code-block:: yaml
+
+    neutron:
+      server:
+        configmap:
+          neutron_server:
+            DEFAULT:
+              max_subnet_host_routes: 30
+              max_routes: 60
+              debug_iptables_rules: True
+            quotas:
+              quota_network: 20
+              quota_subnet: 10
+              quota_port: 100
+            matchmaker_redis:
+              host: 127.0.0.1
+              port: 6379
+              password: pswd
+      gateway:
+        configmap:
+          metadata_agent:
+            DEFAULT:
+              metadata_workers: 10
+              debug: True
+            agent:
+              report_interval: 30
+          l3_agent:
+            DEFAULT:
+              agent_mode : dvr
+            agent:
+              report_interval: 40
+          dhcp_agent:
+            DEFAULT:
+              ovs_vsctl_timeout: 12
+              resync_interval: 60
+            agent:
+              report_interval: 60
 
 Upgrades
 ========