allow use lightning tidb backend to load data to mysql

[glorv]

Feature Request

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

Describe the feature you'd like:

Allow use lightning(tidb backend) to load data to mysql compatible database. So we can completely use lightning to replace myloader.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Optimization:

[glkappe]

Please evaluate the priority of this requirement, it is recommended to bring it in v4.x, otherwise we need to modify the official document

https://docs.pingcap.com/zh/tidb/stable/ecosystem-tool-user-case#%E8%BF%81%E5%87%BA%E6%95%B0%E6%8D%AE%E5%88%B0-mysqltidb

[kennytm]

Please use myloader for now.

To support Lightning (TiDB backend) for MySQL, the first step is to generalize

https://github.com/pingcap/tidb-lightning/blob/2644a194f087372ba94a73df90d5373c00da0b19/lightning/restore/tidb.go#L86-L90

to recognize which variable is causing the "Unknown system variable" error and delete that, not always allow_auto_random_explicit_insert only. Also turn that into a loop.

We'll see what's next after that.

[glkappe]

@kennytm Is the code development progress updated?

[kennytm]

No progress, it is not scheduled for development in this year.