delegate to network of reg services

[pdowler]

for the resource-caps feature, it would be possible to configure one or more external reg services and call them to resolve resourceID lookups... probably pull and cache the remote resource-caps periodically to make a larger network of fast lookups with delegated responsibility.

use case: combine the CADC registry at https://ws.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/reg with one or more external registries (eg https://spsrc27.iaa.csic.es/reg/resource-caps)