This already exists, I have seen it used before, don't know any exact repositories though. The reason it's not really used is because it's pointless. What are you trying to achieve with it? Your community won't look more active if it has more posts with zero upvotes and zero comments all made by the same user.

Hiding posts from bots will also hide posts from this bot.

Keep in mind that not everyone here uses Lemmy, so a Lemmy feature isn't a good defense in a federated world like this.