AI meta data

Work done to make AI supportpower usage slightly smarter. Refer to #5830 

Allows some basic usage rules to be defined in yaml for supportpowers.
Having both `SupportPowerDecision` and `Decision` in the main OpenRA.Mods.RA namespace may be a bit confusing.  This is only used inside `SupportPowerDecision`, so you could move this into an inner class.