Provide password through command

[patrickpichler]

Is your feature request related to a problem? Please describe. There are cases where the password for connecting to a database is provided by a CLI tool such as gcloud.

Describe the solution you'd like It would be useful, if one could specify a passwdCmd, that gets run and its stdout is then used as the password.

Describe alternatives you've considered No alternatives have been considered.

Additional context