Implement role reset and role reassign

[piki]

This adds two new commands to manage roles in Postgres databases:

• pscale role reset --org <org> <db> <branch> <role-id> resets the password for a given role, after prompting for confirmation. It returns the role object with the new password.
• pscale role reassign --org <org> <db> <branch> <donor> --successor <recipient> assigns all objects owned by donor to another role, recipient.

Before merging this:

• merge Add wrappers for role reset and reassign planetscale-go#273
• cut a release of planetscale-go
• bump planetscale-go dependency in go.mod to the new release