docs: Add example job that shuts down proxy containers on completion.

docs/examples/job-mysql.yaml

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+###
+# This demonstrates how to configure a batch job so that it shuts down
+# the proxy containers when it has finished processing.
+#
+# The operator will set an environment variable called CSQL_QUIT_URLS
+# with a space-separated list of URLs to each proxy container's /quitquitquit
+# endpoint. In most cases, your job will only have one proxy container attached,
+# so the value of CSQL_QUIT_URLS will be something like
+# "http://localhost:9091/quitquitquit"
+#
+# The main job container should send a POST request each URL when the job
+# container process finishes. This will cause the proxy side-car containers
+# to shut down.
+#
+# In Kubernetes 1.28, side-car containers will be properly supported. When
+# That happens, we will update the operator to use the built-in side-car
+# mechanism for workloads on clusters version 1.28 and higher.
+#
+# See https://github.com/kubernetes/enhancements/issues/753
+# and https://github.com/GoogleCloudPlatform/cloud-sql-proxy-operator/issues/381
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: job
+  labels:
+    app: busybox
+spec:
+  template:
+    metadata:
+      creationTimestamp: null
+      labels:
+        app: busybox
+    spec:
+      containers:
+      - name: busybox
+        # Run your batch job command.
+        # Then, Iterate through the attached proxy shutdown hooks
+        # set by the operator in $CSQL_QUIT_URLS. Call each proxy's shutdown
+        # hook HTTP endpoint.
+        command:
+        - sh
+        - -c
+        - >
+          psql --host=$DB_HOST --port=$DB_PORT --username=$DB_USER '--command=select 1' --echo-queries --dbname=$DB_NAME
+          
+          for url in $CSQL_QUIT_URLS ; do                               
+            wget --post-data '' $url 
+          done
+        image: busybox
+        imagePullPolicy: IfNotPresent
+        resources: {}
+        terminationMessagePath: /dev/termination-log
+        terminationMessagePolicy: File
+      restartPolicy: Never
+      terminationGracePeriodSeconds: 30
+
+---
+apiVersion: cloudsql.cloud.google.com/v1
+kind: AuthProxyWorkload
+metadata:
+  name: job-proxy
+spec:
+  instances:
+  - connectionString: project:region:instancename
+    hostEnvName: DB_HOST
+    portEnvName: DB_PORT
+  workloadSelector:
+    kind: Job
+    selector:
+      matchLabels:
+        app: busybox