* get_random_community_id: add filters for nsfw and private, use algorithm that doesn't scan the entire table
* only call random_smallint once for filter
* change migration date
* make random_smallint function work in postgresql 16
* replace "32768 + 32767 + 1" with "65536" and improve comments
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Co-authored-by: Dessalines <dessalines@users.noreply.github.com>