billing_plan field deprecation in billable-summary endpoint (#3538)

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.

src/main/java/com/datadog/api/client/v1/model/UsageBillableSummaryHour.java

@@ -116,17 +116,20 @@ public UsageBillableSummaryHour billingPlan(String billingPlan) {
   }
 
   /**
-   * The billing plan.
+   * The billing plan (metadata). (Deprecated from May 2026)
    *
    * @return billingPlan
+   * @deprecated
    */
+  @Deprecated
   @jakarta.annotation.Nullable
   @JsonProperty(JSON_PROPERTY_BILLING_PLAN)
   @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
   public String getBillingPlan() {
     return billingPlan;
   }
 
+  @Deprecated
   public void setBillingPlan(String billingPlan) {
     this.billingPlan = billingPlan;
   }