Adding new documentation type for GaussDB nosql

Reviewed-by: Hasko, Vladimir <vladimir.hasko@t-systems.com>
Co-authored-by: Boka, Ladislav <ladislav.boka@t-systems.com>
Co-committed-by: Boka, Ladislav <ladislav.boka@t-systems.com>

otc_metadata/data/services.yaml

@@ -600,6 +600,14 @@ documents:
     service_type: gaussdb_mysql
     title: User Guide
     type: umn
+  - environment: internal
+    html_location: docs/gaussdb_nosql/api-ref
+    link: /gaussdb_nosql/api-ref/
+    pdf_name: gaussdb_nosql-api-ref
+    rst_location: api-ref/source
+    service_type: gaussdb_nosql
+    title: API Reference
+    type: api-ref    
   - environment: internal
     hc_location: usermanual/nosql
     html_location: docs/gaussdb_nosql/umn