Allocate a new floating IP for the port

Allocates a brand-new floating IP from the external (provider) network pool — the "Allocate new IP" action on the Floating IP tab — and associates it with this port's fixed IP, making the port reachable from the internet. This differs from the attach action, which associates an already-allocated address from the available pool: allocate first carves a new address out of ext-net, then binds it. The association becomes visible on the port (floatingIp field) and in subsequent reads once the operation completes. Validation: the port must exist and be visible in scopeId → ERR_NOT_FOUND otherwise; the port's current state must permit allocation — it must not already have an associated floating IP and must not sit on a public (provider) network, since floating IPs cannot be associated to ports on public networks → ERR_CONFLICT; poolNetworkId, when given, must reference an external network → ERR_VALIDATION (422); the external pool must have free addresses → ERR_CAPACITY when exhausted. Async & state: Asynchronous — 202 with an Operation record. The floating IP is allocated then associated; on success a resource.updated SSE frame patches floatingIp from null to the new address on this network-interface resource. The Operation transitions queued → running → succeeded|failed; failure rolls back the allocation so no orphaned address is billed. Errors: 401 unauthenticated; 403 when the caller lacks contributor/admin rights on the scope; 404 unknown port; 409 CAPACITY_UNAVAILABLE when the external pool has no free addresses (a port that already holds a floating IP or sits on a public network also rejects with 409); 422 on an invalid pool reference; 500 on allocation-control failure. Idempotency/Concurrency: Idempotency-Key required — the UI can retry, and replaying the same key returns the original 202 Operation without allocating a second address.