Missing functions getKeyBy and upsertBy_

[NorfairKing]

getBy and upsertBy load the entire row even when that is sometimes not necessary.
Often I just want to upsert without loading the result.
I would use repsert but that takes a key instead of a uniqueness constraint.

getKeyBy would let me implement upsertBy_ myself.
Alternatively, uniqueToFilters :: Unique record -> [Filter record] would let me do it as well.

CC @parsonsmatt