Prawn -> shrimp alias

BUR #7221 has been approved by @nonamethanks.

create alias prawn -> shrimp

Prawn is the British and Commonwealth English preferred term while shrimp is the American English one. So, alias. The shrimp tag is also more highly populated and has a wiki.

There are some (fisheries and culinary) people that distinguish between the two (by size, anatomical features, habitat, etc), but these criteria change when moving between different English-speaking countries, so no point enforcing the distinction. Not to mention most of the time they aren't visually distinct anyway when drawn.

There's also the prawn crackers tag, which I'm not sure what to do with because it's underpopulated. And topic #19257 cautioning against creating too many tags for different snack items. Maybe alias prawn crackers to chips?

The bulk update request #7221 (forum #196725) has been approved by @nonamethanks.

The prawn crackers tag seem to depict a specific and distinguishable brand of snack, so I think it's fine to have it, in the same way that we have the pringles tag.