InferencePool should have nested status

[robscott]

What happened:
In today's community meeting, @danehans pointed out that it's possible that multiple Gateways will be targeting the same InferencePool.

What you expected to happen:
We should really have a nested status that would allow different Gateways to put different status on InferencePool. This would be similar to Gateway API's RouteStatus.

[robscott]

If anyone with access can add this to a v0.2 milestone, that would be appreciated.

/cc @kfswain @danehans

[ahg-g]

I assume this will require a v1alpha2 update? We also need to rename the port number in the ExtensionRef: #376

[kfswain]

/assign