Add show default quotas API to network quotas_client library

This patch adds show default quotas API to network quotas_client
library and also adds test cases for this feature.

Change-Id: Icadc4a522681ab042ca6e07908bdc16f08330add
diff --git a/releasenotes/notes/add-show-default-quotas-api-to-network-quotas-client-3a7c1159af9e56ff.yaml b/releasenotes/notes/add-show-default-quotas-api-to-network-quotas-client-3a7c1159af9e56ff.yaml
new file mode 100644
index 0000000..6efe7e6
--- /dev/null
+++ b/releasenotes/notes/add-show-default-quotas-api-to-network-quotas-client-3a7c1159af9e56ff.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Add show default quotas API to network quotas_client library.
+    This feature enables the possibility to show default network quotas for
+    a specified project.