docs(kubernetes): add more fleshed-out example of a Demo Kubernetes cluster (#2329)

This Kubernetes cluster has:

- vLLM for serving an inference model
- vLLM for serving a safety model
- Postgres DB (for metadata and other state for the Llama Stack distro)
- Chroma DB for Vector IO (memory)

Perhaps most importantly, this was me trying to learn Kubernetes for the
first time.

## Test Plan

Run `sh apply.sh` against an EKS cluster, then after `kubectl
port-forward service/llama-stack-service 8321:8321` and after many
attempts, we have finally:

<img width="1589" alt="image"
src="https://github.com/user-attachments/assets/c69f242d-6aaa-4def-9f7c-172113b8bfc1"
/>

<img width="1978" alt="image"
src="https://github.com/user-attachments/assets/cf678404-f551-4fa5-9077-bebe3e8e8ae8"
/>

docs/source/distributions/k8s/apply.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+export POSTGRES_USER=${POSTGRES_USER:-llamastack}
+export POSTGRES_DB=${POSTGRES_DB:-llamastack}
+export POSTGRES_PASSWORD=${POSTGRES_PASSWORD:-llamastack}
+
+export INFERENCE_MODEL=${INFERENCE_MODEL:-meta-llama/Llama-3.2-3B-Instruct}
+export SAFETY_MODEL=${SAFETY_MODEL:-meta-llama/Llama-Guard-3-1B}
+
+set -euo pipefail
+set -x
+
+envsubst < ./vllm-k8s.yaml.template | kubectl apply -f -
+envsubst < ./vllm-safety-k8s.yaml.template | kubectl apply -f -
+envsubst < ./postgres-k8s.yaml.template | kubectl apply -f -
+envsubst < ./chroma-k8s.yaml.template | kubectl apply -f -
+
+kubectl create configmap llama-stack-config --from-file=stack_run_config.yaml \
+  --dry-run=client -o yaml > stack-configmap.yaml
+
+kubectl apply -f stack-configmap.yaml
+
+envsubst < ./stack-k8s.yaml.template | kubectl apply -f -
+envsubst < ./ingress-k8s.yaml.template | kubectl apply -f -