Support checksum for dumpling

[lichunzhu]

Feature Request

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

When dumpling finishes dumping progress, it's hard for us to know whether dumpling dumps data correctly.
Describe the feature you'd like:

Support checksum for dumpling to check whether we dump data correctly.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

[lichunzhu]

We can do this by computing checksum of the dumped dumpling files and of tidb by SQL:

select *,  bit_xor(concat(a, b)) over (order by a,b RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) as checksum from t2 where a < 100 order by a,b;