There are a handful of changes in this commit:
* When querying trust bundles for a service we need to be able to
specify the namespace of the service.
* The endpoint needs to track the index because the cache watches use
it.
* Extracted bulk of the endpoint's logic to a state store function
so that index tracking could be tested more easily.
* Removed check for service existence, deferring that sort of work to ACL authz
* Added the cache type
