docs: Update description for ProvisionedService.provisioning_id (#137)

* feat: Change description for GCP ProvisionedService.provisioning_id value feat: Update year from 2021 to 2022

PiperOrigin-RevId: 426206624

Source-Link: googleapis/googleapis@4eca5ca

Source-Link: googleapis/googleapis-gen@a33af8c
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google/cloud/channel_v1/types/entitlements.py

@@ -175,7 +175,9 @@ class ProvisionedService(proto.Message):
         provisioning_id (str):
             Output only. Provisioning ID of the
             entitlement. For Google Workspace, this would be
-            the underlying Subscription ID.
+            the underlying Subscription ID. For Google Cloud
+            Platform, this would be the Billing Account ID
+            of the billing subaccount.".
         product_id (str):
             Output only. The product pertaining to the
             provisioning resource as specified in the Offer.