Docs: Updates getting started guide for kgateway

[danehans]

• Uses tabs to separate implementations.
• Moves Envoy Gateway-specific content to Envoy Gateway tab.
• Adds a Kgateway tab with instructions for using Kgateway as an Inference Gateway.

[k8s-ci-robot]

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[danehans]

I'm using a personal dev build until Kgateway v2.0.0 is cut.

[kfswain]

Do we have an eta on Kgateway's v2.0.0?

[danehans]

3/27

[danehans]

Marked as draft as i validate the steps in the getting started guide.

[danehans]

#552 broke Kgateway integration. Waiting for kgateway-dev/kgateway#10921 to merge for the fix.

[danehans]

I have verified this PR works after kgateway-dev/kgateway#10921 merges. I'm keeping as "draft" until Kgateway v2.0.0 is cut. I will then replace dev build references with v2.0.0.

If you are testing this PR in a cluster that does not support services of type LoadBalancer, do the following:

kubectl apply -f - <<EOF
apiVersion: gateway.kgateway.dev/v1alpha1
kind: GatewayParameters
metadata:
  name: kgateway
  namespace: kgateway-system
spec:
  kube:
    service:
      type: ClusterIP 
---
apiVersion: gateway.networking.k8s.io/v1
kind: GatewayClass
metadata:
  name: kgateway
spec:
  controllerName: kgateway.dev/kgateway
  description: kgateway controller
  parametersRef:
    group: gateway.kgateway.dev
    kind: GatewayParameters
    name: kgateway
    namespace: kgateway-system
EOF

[k8s-ci-robot]

PR needs rebase.

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[ahg-g]

Can we close this now?

[danehans]

Closing since #577 merged.