Added the Thumper

now that we have sandworms https://github.com/OpenRA/OpenRA/pull/6821 and merged medic and engineer into a new support infantry.
I don't think that this case is comparable to gates https://github.com/OpenRA/OpenRA/pull/6907 so I would be glad to hear a more detailed description why this is problematic and what to keep in mind when redoing this.