[WIP] Add CODEOWNERS

[AThousandShips]

Several areas missing but as a starting point to figure out the specifics

[Mickeon]

Is it necessary to specify @godotengine/documentation every time? Can it not be just once, encompassing multiple paths at once?

Edit: I see you've done right just this at the end of the file, so why doing it for every other line?

[AThousandShips]

It cannot be done once only, unfortunately, it would be great if it worked that way but it doesn't

[AThousandShips]

There isn't a specific team for this, so unsure what to add here, ownership is also missing from the main repo for this platform

[Calinou]

I would make them owned by the buildsystem team.

[AThousandShips]

Then I'll add them and see what cases are relevant, might make the root folder buildsystem and filter more finely for the global assignment for documentation

[AThousandShips]

There cleaned up the formatting and added some new entries, will continue next week!