Update Moderation Policy to better handle cases of deleted issues

[aduh95]

It's not rare to document the moderation action as a comment in the same thread, this can be a problem when the issue gets deleted and there's no trace left of the explanation. I suggest to always create an issue in the moderation repo, that way all moderation action are centralized, and not at risk of being victim of collateral damage when spam content is deleted.

//cc @nodejs/moderation @nodejs/tsc