PDI-1632: Add Testing Framework to PingCTL

[erikostien-pingidentity]

• Add/Update cobra command testing to all pingctl commands
• Move all logic from commands to internal definitions for testing and seperation of cobra command configuration.
• Add testing for all internal command logic.
• Remove need for cobra.Command instance in output.go
• Update custom type's valid values function to return list of strings instead of formatted strings, so the function has value in testing.
• Add testing util functions ExecutePingctl() and ExecutePingctlCaptureCobraOutput() to reduce boilerplate when testing cli directly.