Introduce a way to configure servers that can be used to dynamically
update DS records during KSK rollovers. The update-ds configuration
option is a zone only option and may reference a parental-agents
statement.
Add some checkconf checks similar to parental-agents, like the option
being at the wrong level, a duplicate list, an empty list, at the
wrong zone type, and a reference to parental-agents not found.
24d9677c0f