Inference Extension: add NGF to Inference docs

[sjberman]

The inference extension docs mention various implementations that support the API. For example, the Getting Started guide. NGF should have a presence there once we release with Inference Extension support.

Any other locations in the docs that mention supported implementations should also be updated.
eg: https://gateway-api-inference-extension.sigs.k8s.io/implementations/gateways/

Acceptance

• once released, NGF should be present in the Gateway API inference extension docs.
• add inference conformance report to their repo