secrets API: add list secret scopes

proto/redpanda/api/dataplane/v1alpha2/secret.proto

@@ -201,6 +201,15 @@ message DeleteSecretRequest {
 // DeleteSecretResponse is the response of DeleteSecret.
 message DeleteSecretResponse {}
 
+// ListSecretScopesRequest is the request of ListSecretScopes.
+message ListSecretScopesRequest {
+}
+
+// ListSecretScopesResponse is the response of ListSecretScopes.
+message ListSecretScopesResponse {
+  repeated Scope scopes = 1;
+}
+
 // Connect Secrets API
 
 // GetConnectSecretRequest is the request of GetSecret.
@@ -533,6 +542,24 @@ service SecretService {
     };
   }
 
+  // ListSecretScopes lists the supported secret scopes.
+  rpc ListSecretScopes(ListSecretScopesRequest) returns (ListSecretScopesResponse) {
+    option (google.api.http) = {get: "/v1alpha2/secret-scopes"};
+    option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+      summary: "List Secret Scopes"
+      description: "List supported secret scopes."
+      responses: {
+        key: "200"
+        value: {
+          description: "OK"
+          schema: {
+            json_schema: {ref: ".redpanda.api.dataplane.v1alpha2.ListSecretsScopesResponse"}
+          }
+        }
+      }
+    };
+  }
+
   // Connect Secrets API.
 
   // GetConnectSecret retrieves the specific secret for a specific Connect.