TiChi controll post-merge CI builds on pingcap/tidb repo

Hi everyone,

We are happy to announce that the pingcap/tidb repository’s master branch is now using TiChi bot to manage the postsubmit tasks. This change will make it easier to view the execution status and results of all or some of the pipelines.

We hope that this adjustment will be helpful to the community and we welcome any feedback you may have.

Thank you for your continued support.

Best regards,