Command to undelegate from validators

Have a command that you can undelegate from a validator and also with the option `--all` that generate multiple transactions each with around 5 messages (one message per validator).

Start by locating the existing delegation and transaction-building command entry points. Determine how validator selections and transaction messages are currently represented, then verify that an undelegation command supports one validator and that --all groups roughly five validator messages per transaction. Done means the command produces the expected undelegation transactions for both modes.

Written by the indexing model from the issue text.