Publish the bound NetworkInterface on Instance status

[scotwells]

Adds Instance.status.networkInterfaces[].networkInterfaceRef: the NetworkInterface bound to that entry, in the instance's namespace.

Something configuring the attachment needs the interface the instance ended up with. Without a published reference it has to reconstruct compute's private networkInterfaceClaimName to find the claim first — the Unikraft provider currently carries a verbatim copy of that function, sha256 truncate-and-hash fallback included, in another repo. A private naming convention duplicated across repos breaks silently the day it changes.

The reader is now the VPC controller's Pod admission webhook rather than the infrastructure provider: the webhook resolves a Pod to its Instance, follows this reference to each interface, and injects whatever the delivery mechanism requires. Same reason for the field, one fewer component that has to know how compute names things — and with the provider out of that path entirely, the duplicated function is deleted rather than merely unused.

The change is a passthrough: reconcileNetworkInterfaceStatus already reads the claim to publish addresses and conditions, and the claim already carries status.networkInterfaceRef.

The field reuses NSO's existing LocalNetworkInterfaceRef rather than declaring a compute-local struct, so anything following the chain from Instance to interface handles one shape rather than two.

Not in this change: the capability class that decides how a guest consumes the NIC. That is a product API decision tracked separately.

make lint clean; full unit suite (non-e2e, with envtest) green. docs/api is generated and already drifted on main, so it is left untouched to keep the diff to the change itself.

Related

• Umbrellas: Integrate IPAM and compute networking interface network-services-operator#164, Integrate with network services operator for IP address assignment #112
• First consumer, and the new reader: feat(vpc): add the VPC controller that realizes attachments on the data plane cloud#6
• Siblings: Add a Prepared condition, and attachmentMode on the claim network-services-operator#393, Gate the network on Prepared, never on Programmed #244

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