Proposal: an OCI-SessionID header on all requests originating from the same image push/pull

[suleimi]

After trying to debug some inconsistent behaviour between a registry and one of its client, I realized there is value in having client-side propagate a uniquely generated sessionID to registries to identify all requests initiated through a logical (push/pull) operation from a CLI's/users perspective . This proposed uniquely generated session id (per push/pull) can be used in registries to group sets of requests for tracing or debugging purposes.

I believe this will benefit a lot in debugging issues originating from clients and in correlating traces with https://opentracing.io/.