CDC clould: grafana -> TiCDC ->Changefeed -> Changefeed checkpoint lag, display issue

[Tammyxia]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error.

• Grafana -> TiCDC, last 3 hours.

2. What did you expect to see?

3. What did you see instead?

• TiCDC ->Changefeed -> Changefeed checkpoint lag
  

4. Versions of the cluster

   • Upstream TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

     4.0.14
     

   • TiCDC version (execute cdc version):

     # ./cdc version
     

Release Version: 4.0.14
Git Commit Hash: bbfda29
Git Branch: cloud-cdc-4.0
UTC Build Time: 2021-08-26 14:08:37
Go Version: go version go1.16.3 linux/amd64
Failpoint Build: false

    ```

[Tammyxia]

The display for Processor resolved ts lag is not match with checkpoint lag.