Handle the hardcoded configuration values

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

  barbican:
    server:
      configmap:
        DEFAULT:
          max_allowed_secret_in_bytes: 10000
          max_allowed_request_size_in_bytes: 1000000
          sql_pool_max_overflow: 10
          default_limit_paging: 10
          max_limit_paging: 100
        quotas:
          quota_secrets: -1
          quota_orders: -1
          quota_containers: -1
          quota_consumers: -1
          quota_cas: -1

Change-Id: Ibef6f409396bb862436ac747e4fa7cf3564d8eff
Related-Prod: PROD-29627
diff --git a/README.rst b/README.rst
index 0557f46..904bf22 100644
--- a/README.rst
+++ b/README.rst
@@ -460,6 +460,27 @@
             strategy: ENCRYPT
             secret_key: secret
 
+Change default options using configmap template settings
+========================================================
+
+.. code-block:: yaml
+
+  barbican:
+    server:
+      configmap:
+        DEFAULT:
+          max_allowed_secret_in_bytes: 10000
+          max_allowed_request_size_in_bytes: 1000000
+          sql_pool_max_overflow: 10
+          default_limit_paging: 10
+          max_limit_paging: 100
+        quotas:
+          quota_secrets: -1
+          quota_orders: -1
+          quota_containers: -1
+          quota_consumers: -1
+          quota_cas: -1
+
 Read more
 =========