enable rotation of custody password

[redshiftzero]

Is your feature request related to a problem? Please describe.
As of #4343, there is an option to encrypt the custody config file with a password such that it is encrypted at rest.
However we don't currently provide a way to rotate that password.

Describe the solution you'd like
Let the user rotate the custody password, perhaps modifying or extending the existing pcli init re-encrypt command.