Add a network traffic tab to Gateway resources so that traffic can be visualised in a filtered way more easily

The tab would behave similar to other network traffic tabs, but be filtered to traffic going through that Gateway to various backend services (configured in HTTPRoutes)

Gateways are set as the ownerRef on Deployments for gateway pods (envoy proxy).

Here's an example of the ownerRef chain from the envoy proxy pod back to the Gateway

https://gist.github.com/david-martin/d9a3bd1f67c176bd93ecf5b31f889ee1