The classic way to drill a hole like this is to use a machinist scribe to scratch a small t where you want the hole. Optionally, you use little pieces of metal called seat rule clamps on your metal machinist's rule to ensure that your "t" is centered on the tube. Then you'd use a prick punch (yes, that's what its called) with a small ball pein hammer to put a little dent into the tube. Then if the small dent was exactly where you wanted it you'd use a center punch and hammer to make the divot larger. This divot would guide a 1/16" or 3/32 (1 mm) guide drill. At which point you could use the appropriate sized drill for an M5 rivnut (which is usually a 7mm +0.1/-0.0 hole - for which you might use a slightly smaller drill because hand drills yield holes larger than nominal). Steel rivnut for steel frame, aluminum or stainless steel rivnut for aluminum frame.
There's a good discussion relevant to the OP's question
here. There's a suggestion to use rubber molding compound to make a shock-absorbing gasket. Anyway, some ideas.
Also, there's many different installation tools, some industrial ones ranging into the thousands of dollars. A simple, fairly cheap tool is listed
here. I have no experience with this but it looked pretty nice - you have the mechanical advantage of the inclined plane coupled with the MA of the screw. Anyone used this tool?