Alias rkgk to sketch

BUR #61049 has been rejected.

create alias rkgk -> sketch

#rkgk is the hashtag some artists use for their sketches especially on Twitter and Pixiv. I believe it deserves an alias for ease of access. It will also redirect wiki searches for rkgk to sketch which would be informative.

This seems pretty unnecessary. A lot of artists just slap rkgk onto everything, including many things we would not call "sketch", and nobody is actually searching "rkgk" on danbooru.

The bulk update request #61049 (forum #445038) has been rejected by @nonamethanks.