Make the automated "vote cleaner" self-service

There's a vote cleaner that periodically removes what look like duplicate votes, based on IP address.

Currently this is enabled by the Feature Upvote team for a board upon request.

This could be made self-service, so that any board main can enable it.

WARNING: In some companies, all the users appear to be coming from the same IP address, and might be detected as duplicate votes. If we add this, we'll need to make the risks very clear .