Patches metadata on up to 1,000 customers in one atomic request. Each customer may receive
different values. If a customer is missing or any key or value is invalid, nothing is
written for any customer. Per customer this behaves exactly like patch-customer-metadata:
keys omitted for that customer are left unchanged; null, empty, and whitespace-only values
clear that key.
Metadata-only changes are recorded in the audit log but do not trigger customer.updated
webhooks or customer integration syncs.