fix: proton

Author: Yash bhardwaj

gotocompany/optimus/core/v1beta1/backfill.proto

@@ -104,11 +104,13 @@ message BackfillSpec {
   string namespace_name                = 4;
   string job_name                      = 5;
   string description                   = 6;
+
   google.protobuf.Timestamp data_start_time = 7;
   google.protobuf.Timestamp data_end_time   = 8;
   google.protobuf.Timestamp start_time      = 9;
   google.protobuf.Timestamp end_time        = 10;
-  string custom_assets                 = 11;
+
+  map<string, string> custom_assets    = 11;
   string job_config                    = 12;
   string status                        = 13;
   string message                       = 14;