Add metadata for OMS - Object Storage Migration Service

Adds service metadata for OMS (Object Storage Migration Service)
in the storage category, including API and UMN document types.

Resolves #101

otc_metadata/data/documents/oms-api-ref.yaml

@@ -0,0 +1,13 @@
+---
+hc_location: api/oms
+html_location: docs/oms/api-ref
+link: /object-storage-migration-service/api-ref/
+rst_location: api-ref/source
+service_type: oms
+title: API Reference
+type: api-ref
+cloud_environments:
+  - name: eu_de
+    visibility: public
+    pdf_visibility: public
+    pdf_enabled: true