Create a dedicated endpoint for COSE service identity endorsement verification

[maxtropets]

@maxtropets we should have an endpoint that takes a historical service identity, and returns the chain of endorsements up to the current service, if found, and a clear message otherwise. This will be useful for users who have large amounts of receipts, and want to quickly check/confirm that a new service endorses them.

We also want a CDDL schema of the endorsements, with an automatic test, and Merkle root chaining as discussed.

Originally posted by @achamayou in #6500