billing_plan field deprecation in billable-summary endpoint (#3556)

Co-authored-by: ci.datadog-api-spec <packages@datadoghq.com>

Author: api-clients-generation-pipeline[bot]

.generator/schemas/v1/openapi.yaml

@@ -20019,7 +20019,8 @@ components:
           description: The account public ID.
           type: string
         billing_plan:
-          description: The billing plan.
+          deprecated: true
+          description: The billing plan (metadata). (Deprecated from May 2026)
           type: string
         end_date:
           description: Shows the last date of usage.

services/usage_metering/src/v1/models/UsageBillableSummaryHour.ts

@@ -15,7 +15,7 @@ export class UsageBillableSummaryHour {
    */
   "accountPublicId"?: string;
   /**
-   * The billing plan.
+   * The billing plan (metadata). (Deprecated from May 2026)
    */
   "billingPlan"?: string;
   /**