refactor: deprecate billing_id in entitlement and usage RPCs

Mark billing_id field as deprecated in the following RPCs:
- CheckFeatureEntitlement
- CreateBillingUsage
- RevertBillingUsage

The billing_id will now be automatically inferred from org_id on the backend.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: whoAbhishekSah

raystack/frontier/v1beta1/admin.proto

@@ -1098,12 +1098,14 @@ message RevertBillingUsageRequest {
   string org_id = 1;
   string project_id = 2;
 
-  // either provide billing_id of the org or API can infer the default
-  // billing ID from either org_id or project_id, not both
-  string billing_id = 3 [(validate.rules).string = {
-    ignore_empty: true,
-    uuid: true
-  }];
+  // DEPRECATED: billing_id will be inferred from org_id
+  string billing_id = 3 [
+    deprecated = true,
+    (validate.rules).string = {
+      ignore_empty: true,
+      uuid: true
+    }
+  ];
 
   // usage id to revert, a usage can only be allowed to revert once
   string usage_id = 4 [(validate.rules).string = {uuid: true}];

raystack/frontier/v1beta1/frontier.proto

@@ -2030,11 +2030,14 @@ message HasTrialedResponse {
 
 message CreateBillingUsageRequest {
   string org_id = 1;
-  // ID of the billing account to update the subscription for
-  string billing_id = 2 [(validate.rules).string = {
-    ignore_empty: true,
-    uuid: true
-  }];
+  // DEPRECATED: billing_id will be inferred from org_id
+  string billing_id = 2 [
+    deprecated = true,
+    (validate.rules).string = {
+      ignore_empty: true,
+      uuid: true
+    }
+  ];
 
   // either provide billing_id of the org or API can infer the default
   // billing ID from either org_id or project_id, not both
@@ -2253,11 +2256,14 @@ message ListPlansResponse {
 
 message CheckFeatureEntitlementRequest {
   string org_id = 1;
-  // ID of the billing account to update the subscription for
-  string billing_id = 2 [(validate.rules).string = {
-    ignore_empty: true,
-    uuid: true
-  }];
+  // DEPRECATED: billing_id will be inferred from org_id
+  string billing_id = 2 [
+    deprecated = true,
+    (validate.rules).string = {
+      ignore_empty: true,
+      uuid: true
+    }
+  ];
 
   // either provide billing_id of the org or API can infer the default
   // billing ID from either org_id or project_id, not both