#1309 prosodyctl comand to show what DNS records to add
Description of feature:
A new `prosodyctl dns` command that generates the DNS records needed, based on the current configuration.
DNS configuration is one of the things that are still tricky for new (and old) users.
A command that shows what records to insert would go a long way.
`prosodyctl check dns` might have some code that could be shared.
This shouldn't be too hard on its own, so marking it as easy.