[FLINK-38124][docs] Add README for Autoscaling example (#1024)

Author: kaygorodov

examples/autoscaling/README.md

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+
+# Flink Kubernetes Autoscaling Example
+
+## Overview
+
+This example contains two Flink applications showcasing the Flink Autoscaler capabilities:
+
+- `AutoscalingExample.java` with its accompanying `autoscaling.yaml` containing the `FlinkDeployment` definition
+- `LoadSimulationPipeline.java` with its accompanying `autoscaling-dynamic.yaml` containing the `FlinkDeployment` definition
+
+Both applications are packaged into a single fat jar, which is then included in a Docker image
+built from the provided `Dockerfile`.
+
+### AutoscalingExample
+
+This application contains a source that emits long values, a map function with an emulated
+processing load, and a discard sink. The processing load per record can be configured by
+adjusting the job argument in `autoscaling.yaml`:
+
+```
+job:
+  args: ["10"]
+```
+
+The argument value specifies how many synthetic iterations are performed for each record.
+
+### LoadSimulationPipeline
+
+This application simulates fluctuating load that could be configured via the job arguments in 
+`autoscaling-dynamic.yaml`:
+
+```
+job:
+    args:
+    - --maxLoadPerTask "1;2;4;8;16;\n16;8;4;2;1\n8;4;16;1;2" --repeatsAfterMinutes "60"
+```
+
+Refer to `LoadSimulationPipeline.java`'s JavaDoc and comments for the details concerning the argument
+notation and simulated load pattern.
+
+## Usage
+
+The following steps assume that you have the Flink Kubernetes Operator installed and running in 
+your environment. If not, please follow the Flink Kubernetes Operator [quickstart](https://nightlies.apache.org/flink/flink-kubernetes-operator-docs-main/docs/try-flink-kubernetes-operator/quick-start/) to start with.
+
+**Step 1**: Build Autoscaling example maven project
+```bash
+cd examples/autoscaling
+mvn clean package
+```
+
+**Step 2**: Build docker image
+```bash
+# Uncomment when building for local minikube env:
+# eval $(minikube docker-env)
+
+DOCKER_BUILDKIT=1 docker build . -t autoscaling-example:latest
+```
+
+This step will create an image based on an official Flink base image including the Autoscaling application jar.
+
+**Step 3**: Only for AutoscalingExample: Mount volume to keep savepoints and checkpoints
+
+```bash
+# Assuming minikube is used for local testing or alternatively ensure any other k8s cluster setup with access to a persistent volume
+mkdir /tmp/flink # or any other local directory
+minikube mount --uid=9999 --gid=9999 /tmp/flink:/tmp/flink
+```
+
+**Step 4**: Submit FlinkDeployment Yaml
+
+For *AutoscalingExample*:
+
+```bash
+kubectl apply -f autoscaling.yaml
+```
+
+or for *LoadSimulationPipeline*:
+
+```bash
+kubectl apply -f autoscaling-dynamic.yaml
+```