Well, that second paragraph sort of answers the question. There may be situations where I'd like to turn the lights off. I'd rather have a switch and not need it than to need a switch and not have it.
You have everything you need for auto-on/off with the ignition and at-will off with the switch. (Though I see below you don't want to drill any holes to mount the switch that came with the harness -- there are plenty of options for handlebar-mounted switches on from Stromtrooper vendors or Amazon.) In this thread
, the first diagram (deleting the smaller box in the top right) will get you the above setup.
I'm all thumbs, and did the above, just without the switch. I positioned my relay under the seat and tapped the switched +12v tail light wire, since I didn't opt for an accessible switch to turn my lights off.
In your case, you could position the relay and tap a switched +12v wire near the switch position (likely handlebars). Main power and ground wires for the lights will run from the relay to the lights, and from the relay back to the battery as indicated in the diagram.
I usually just use positaps and posilocks for my connections. If concerned about weather exposure, I add a layer of shrinkwrap. You'll want to position the relay somewhere out of the way, of course, and if concerned about weather exposure could wrap it in leftover inner tube rubber or some such (or get a water resistant relay).