Minor change to generate report command syntax (using is no more an option)

There is a minor change introduced to the generate report command syntax.

Given that --using option is mandatory, it was decided to include it into the command "body":

• Old syntax: opentf-ctl generate report {workflow_id} --using={file} --name={insight} --save-to={destination}
• New syntax: opentf-ctl generate report {workflow_id} using={file} --name={insight} --save-to={destination}

--name and --save-to remain optional.