Support writing to cloud storage (S3, GCS, ...)

[kennytm]

We should be able to reuse the fruit from pingcap/br#89.

Score

• 450

[IANTHEREAL]

I need to determine if we develop an SQL based export feature for tidb, what tool will we choose to implement, dumpling or br?

• The positioning of dumpling is an export tool for various heterogeneous databases.

• BR also has plans to back up multiple data formats, such as csv

The reason is that br is better in implementation than dumpling, has a more complete flow control mechanism, and scalable performance, support more other features (cloud storage)

@overvenus