feat(auth): emit OCSF events for credential-less gateway requests

Requests the gateway rejects before consulting any authenticator now emit
an OCSF Authentication [3002] event: no credential presented, mTLS
required without a client certificate, or an operator certificate
combined with an authorization header. Each event carries a reason
category in status_detail and never the presented credential. The
response returned to the caller is unchanged.

openshell-ocsf gains the Authentication class with user and service
objects, and a shared OcsfCapture test layer. Schema validation now
rejects attributes the class does not define and profile attributes
whose profile the event does not declare.

Refs #2912

Signed-off-by: Kris Hicks <khicks@nvidia.com>

Author: krishicks