Currently within x/distribution/client/cli/tx.go : GetCmdWithdrawRewards a delegator can only withdraw from one validator at a time... infact there isn't an early check to ensure that the validator input is provided - it will just error when it tries to parse the validator from "".

The old distribution CLI had a "withdraw all path" which was the default and didn't require a validator address - we should reimplement this for F1 as well as a "withdraw all as well as my commission" for validators.

This can be implemented as either multi-transaction (of the existing message types) or a new "withdraw all" msg types within distribution.

CC @cwgoes @alessio