Additional Resolve Modes

[zachmann]

Improve the resolver with additional resolve modes:

• Scheduled: A resolve mode that resolves entities only for a list of allowed trust anchors; the resolver periodically resolves all entities under that trust anchors and keeps the result in cache. Responses are always from cache.
• Delegated: Resolver needs a mapping which (leaf) entities are under which subordinate. Resolver will go to the relevant subordinate's resolve endpoint and that resolver will resolve the entity. Then we only adjust the response to include ourself.