This window kit gives you that instantly.
First drill holes for rivet nuts.
The rivet nuts require a hole that is just over the diameter of the nut. That is 6mm or about 1/4 inch. Test your drill and the rivet nut for a good fit before drilling the door.
Next cut the opening in your door.
This can be done with several different tools. I tried a nibbler but it throws tiny metal shards everywhere. A simple sabre saw will do as well but the cut is usually more ragged. A metal cutting blade on a saw or rotary tool is the cleanest.
Next install the rivet nuts.
For a good look at how to install a rivet nut see this YouTube page – https://www.youtube.com/watch?v=4O-8wF3m1Gc
Just note that the diameter of 13 mm in the video is not for this rivet nut.