fix(extensibility): use ConsumptionLevel for UMS destination lookup

The UMS transport passed Level.SUB_ACCOUNT to get_destination(), which
appends '@SUB_ACCOUNT' to the URL path. The Destination Service V2 API
rejects this with HTTP 400 because it expects lowercase level hints.

Use ConsumptionLevel.PROVIDER_SUBACCOUNT instead, which resolves to
'@provider_subaccount' — the correct value for provider-scoped
destinations like the UMS mTLS destination.

Author: steffensa

src/sap_cloud_sdk/extensibility/_ums_transport.py

@@ -23,7 +23,7 @@
 
 import httpx
 
-from sap_cloud_sdk.destination import Level
+from sap_cloud_sdk.destination import ConsumptionLevel
 from sap_cloud_sdk.destination import create_client as create_destination_client
 from sap_cloud_sdk.extensibility._models import (
     DEFAULT_EXTENSION_CAPABILITY_ID,
@@ -540,7 +540,8 @@ def get_extension_capability_implementation(
         # 1. Resolve destination -----------------------------------------
         try:
             dest = self._dest_client.get_destination(
-                self._destination_name, level=Level.SUB_ACCOUNT
+                self._destination_name,
+                level=ConsumptionLevel.PROVIDER_SUBACCOUNT,
             )
         except Exception as exc:
             raise TransportError(