Add option to indicate you're a prime member for prime-only amazon deals

Sometimes, items go on sale for prime members only. It’d be nice if DD was able to detect prime-only sales, and if you’ve indicated you’re a member, alert you if it matches all other criteria normally.

I would like to see this as well now that Deku supports opt-in stores. Amazon has the low price ever for Pragmata right now if you have Prime.

Also, same thing for Walmart+