Ported mission GDI03 to the new Lua API

Followup of https://github.com/OpenRA/OpenRA/pull/6786, https://github.com/OpenRA/OpenRA/pull/6769 and https://github.com/OpenRA/OpenRA/pull/6762.
You can avoid the notification sounds playing at the start of the intro video (and then timing out by the end of it) by adding them as an after-movie function:

```lua
	Media.PlayMovieFullscreen("samdie.vqa", function()		
		nodObjective = enemy.AddPrimaryObjective("Destroy all GDI troops")
		gdiMainObjective = player.AddPrimaryObjective("Eliminate all Nod forces in the area")
		gdiAirSupportObjective = player.AddSecondaryObjective("Destroy the SAM sites to receive air support")
	end)
```