chore(helm): update pipeline db version to 21 (#1050)

Because

- The pipeline db version need to be updated.

This commit

- Updates pipeline db version to 21

charts/core/values.yaml

@@ -388,7 +388,7 @@ pipelineBackend:
   # -- The path of configuration file for pipeline-backend
   configPath: /pipeline-backend/config/config.yaml
   # -- The database migration version
-  dbVersion: 19
+  dbVersion: 21
   # -- workflow setting
   workflow:
     maxWorkflowTimeout: 3600 # in seconds