always pull the old value internally

[hi-rustin]

Feature Request

Is your feature request related to a problem? Please describe:

Because our new collation feature needs the old value to work properly. However, some users will not use old value, but may use new collation, so it needs to be configured by the user. (Users don't even know if they have new collation on)

To simplify this configuration and to make it easier for the user, we decided to:

1. always use old value internally.
2. the data output to the user needs to be in the correct format (without the old value configuration on, the old value cannot be output)

Describe the feature you'd like:
ticdc always pull the old value internally.

Describe alternatives you've considered:
None

[hi-rustin]

A more detailed document: https://github.com/SuperSupeng/TIDB-tutorial/blob/main/content/TiCDC/%E9%9C%80%E6%B1%82/oldValue.md

From: @SuperSupeng ❤️

[hi-rustin]

cc: #2073

This seems to be the same requirement? @pepezzzz

[amyangfei]

Closed by #2367