Create missing car/docs/data_model/http.md file

[InfiniteInsight]

I noticed there was a 404 error when trying to view https://car.mitre.org/data_model/http so I created it based off of the car/data_model/http.yml file

There are also minor formatting fixes to line breaks in various coverage map tables as in example: car/docs/data_model/registry.md line 36, etc.

This is my first PR on github period, if I've done something incorrectly feel free to let me know. Thanks.

[InfiniteInsight]

Fingers crossed 🤞 Hope this helps