Add `ip_pool_id` to floating IP response

[david-crespo]

It's on the model:

omicron/nexus/db-model/src/external_ip.rs

Lines 204 to 214 in c1f9e8f

	pub struct FloatingIp {
	#[diesel(embed)]
	pub identity: FloatingIpIdentity,
	pub ip_pool_id: Uuid,
	pub ip_pool_range_id: Uuid,
	pub is_service: bool,
	pub parent_id: Option<Uuid>,
	pub ip: IpNetwork,
	pub project_id: Uuid,
	}

But not on the view:

omicron/nexus/types/src/external_api/views.rs

Lines 448 to 458 in c1f9e8f

	pub struct FloatingIp {
	#[serde(flatten)]
	pub identity: IdentityMetadata,
	/// The IP address held by this resource.
	pub ip: IpAddr,
	/// The project this resource exists within.
	pub project_id: Uuid,
	/// The ID of the instance that this Floating IP is attached to,
	/// if it is presently in use.
	pub instance_id: Option<Uuid>,
	}

It would be trivial to add and we think we want this info on the frontend. For example, imagine there are two pools linked to a silo, one with public IPs and one with private IPs. You would want to know which pool a floating IP came from. Right now you'd have to put it in the name or description.