NewCommand creates a new cobra command for showing the details of a resource group, with flags for resource group,
workspace, and output. It returns the command and a Runner to execute the command.
Run creates an ApplicationsManagementClient, retrieves a resource group, and writes the resource group to an
output, returning an error if any of these steps fail.
Validate checks the command line arguments, workspace, output format, and resource group, and sets the
corresponding fields in the Runner struct. It returns an error if any of these checks fail.