NewCommand creates a new cobra command for deleting a workspace, with flags for workspace name and confirmation, and
returns it along with a Runner to execute the command.
Run prompts the user to confirm the deletion of a workspace, and if confirmed, deletes the workspace from the
config file, returning an error if one occurs.
Validate checks if the workspace is valid and sets the workspace and confirmation flags accordingly, returning
an error if the workspace is not stored in configuration.