Require more batch operations for TransactionClient

[blacktear23]

Require more batch operations for TransactionClient such as RawClient did. Such as:

• batch_put
• batch_scan
• batch_delete
• delete_range

[ekexium]

Hi, do you need them in your application?

batch_scan in transaction API is not supported by TiKV. If you really want it, please submit a feature request to tikv/tikv.

For optimistic transactions, batch_delete and batch_put are equivalent to multiple deletes and puts .
For pessimistic transactions, a more efficient way is first lock_keys and then do multple deletes or puts. Maybe we could provide an friendlier interface to do this.

There exists a delete_range request supported by TiKV, and client-rust hasn't implemented it.