Support draft-ietf-rats-coserv-03

[thomas-fossati]

The corim/coserv package has been recently updated to support version 03 of the specification.

This version introduces a breaking change to the wire format.

This issue tracks the implementation of -03 in the coserv service.

[thomas-fossati]

Currently, a couple of features ("CCA/PSA refresh" and "CoRIM stores") are being merged into the mainline in both the veraison/corim and veraison/services areas, causing churn around the coserv area.

In order to assemble a deployable service that supports coserv-03 without altering the CCA endorsement format consumed by existing coserv clients, we will temporarily carve out a couple of special branches in veraison/corim (coserv-03-pre-cca-update) and veraison/services (coserv-03).

This is just a stopgap. Once the "CCA/PSA refresh" and "CoRIM stores" features have been merged and stabilised, we can work on a clean update.