rename http status codes

Posted under Tags

BUR #59345 has been approved by @evazion.

rename 403 -> http_403
rename 404 -> http_404
rename 500 -> http_500

some of these are recognizable such as 404 being a famous code, but i think in general it's poor form to have tags that are just numbers. the thing that pushed me to make this bur was @Historyanon removing the 500 tag from post #11055128, i assume because just the number 500 by itself looks like an invalid tag, despite it being an accurate description of the post.

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