Support generate undo SQL from TiCDC log

[3pointer]

Feature Request

Describe your feature request related problem:

Part of #325, After https://github.com/pingcap/ticdc/issues/768 TiCDC support external storage.

BR then has the ability to decode the log data to a Undo SQL. This usually needed, when user want to rollback one transaction. For example, after execute delete/update succeed, found that the where clause was wrong.

Describe the feature you'd like:

Support generate Undo SQL from TiCDC log.

1. The log data format according to TiCDC open protocol.
2. Use BR to translate the row changed events then spell out the Undo SQL with given ts range.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

Workload estimation(person-day)

• Design: 1
• Develop: 3
• QA: 3
• Document: 3

[FateTHarlaown]

Hi，is there a plan about when to develop this feature?:)