Investigate and remove unmanaged 'datum' GatewayClass from project control planes

[drewr]

Problem

During incident datum-cloud/engineering#258, a gateway was created with spec.gatewayClassName: datum. This class exists in project control planes but has no backing controller. Its origin is unknown — it may be a legacy class, a planned-but-unimplemented class, or a misconfiguration.

Actions Needed

1. Determine where the datum GatewayClass is registered and what created it.
2. If it has no controller and is not planned, remove it from all project control planes.
3. If it is planned, either implement a controller for it or block it from being used until one exists.

Impact

As long as datum exists as a GatewayClass, users can create gateways that will silently never be programmed.