BE-416: Add Constant::JsonNull, remove Constant::String, add From impls#8468

TimDiekmann merged 4 commits intomainhashintel/hash:mainfrom

t/be-416-allow-for-a-more-diverse-set-of-constant-values-in-querieshashintel/hash:t/be-416-allow-for-a-more-diverse-set-of-constant-values-in-queriesCopy head branch name to clipboard