Alias liminal space to backrooms tag

BUR #11469 has been rejected.

create alias liminal_space -> backrooms_(creepypasta)

"Liminal space" is another popular name used to refer to backrooms image.

Liminal space exists as a concept outside of and predates the Backrooms meme, I would imagine something could be Liminal space without actually being a reference to the meme.

The bulk update request #11469 (forum #217800) has been rejected by @nonamethanks.