chore(doc): add some examples for driver configuration (#125)

docs/user-guide/examples.md

@@ -68,3 +68,176 @@ or using the CLI:
 ```bash
 --8<-- "examples/java/submit.sh"
 ```
+
+### Driver configuration
+
+This package manages Spark applications in Kubernetes by directly creating the driver pod and submitting the job in client mode. This approach bypasses some of Spark's built-in driver configuration mechanisms, causing certain settings to be ignored (e.g., `spark.kubernetes.driver.podTemplateFile`, `spark.kubernetes.driver.label.[LabelName]`, ...).
+
+To address this, the package provides internal implementations for some key driver configurations, ensuring greater control and flexibility when deploying Spark applications in Kubernetes.
+
+#### Driver service account
+Instead of providing `spark.kubernetes.authenticate.driver.serviceAccountName=<some-service-account>`, you can use:
+```python
+spark_client.submit_app(
+    ...,
+    service_account="<some-service-account>",
+)
+```
+
+#### Driver resources
+Instead of providing `spark.driver.memory`, `spark.driver.cores`, `spark.driver.memoryOverhead`, you can use:
+```python
+from spark_on_k8s.client import PodResources
+
+spark_client.submit_app(
+    ...,
+    driver_resources=PodResources(cpu=1, memory=512, memory_overhead=128),
+)
+```
+
+#### Driver environment variables
+Instead of providing `spark.kubernetes.driverEnv.[EnvironmentVariableName]=<some-value>`, the package provides a safer way by creating an ephemeral secret and mounting it as an environment variable in the driver pod:
+```python
+spark_client.submit_app(
+    ...,
+    secret_values={"EnvironmentVariableName": "some-value"},
+)
+```
+
+#### Driver volume mounts
+Instead of providing `spark.kubernetes.driver.volumes`, `spark.kubernetes.driver.volumeMounts`, you can use:
+```python
+from kubernetes import client as k8s
+
+spark_client.submit_app(
+    ...,
+    volumes=[
+        k8s.V1Volume(
+            name="volume1",
+            host_path=k8s.V1HostPathVolumeSource(path="/mnt/volume1"),
+        ),
+        k8s.V1Volume(
+            name="volume2",
+            empty_dir=k8s.V1EmptyDirVolumeSource(medium="Memory", size_limit="1Gi"),
+        ),
+        k8s.V1Volume(
+            name="volume3",
+            secret=k8s.V1SecretVolumeSource(
+                secret_name="secret1", items=[k8s.V1KeyToPath(key="key1", path="path1")]
+            ),
+        ),
+        k8s.V1Volume(
+            name="volume4",
+            config_map=k8s.V1ConfigMapVolumeSource(
+                name="configmap1", items=[k8s.V1KeyToPath(key="key1", path="path1")]
+            ),
+        ),
+        k8s.V1Volume(
+            name="volume5",
+            projected=k8s.V1ProjectedVolumeSource(
+                sources=[
+                    k8s.V1VolumeProjection(
+                        secret=k8s.V1SecretProjection(items=[k8s.V1KeyToPath(key="key1", path="path1")])
+                    ),
+                    k8s.V1VolumeProjection(
+                        config_map=k8s.V1ConfigMapProjection(
+                            items=[k8s.V1KeyToPath(key="key1", path="path1")]
+                        )
+                    ),
+                ]
+            ),
+        ),
+        k8s.V1Volume(
+            name="volume6",
+            nfs=k8s.V1NFSVolumeSource(server="nfs-server", path="/mnt/volume6", read_only=True),
+        ),
+        k8s.V1Volume(
+            name="volume7",
+            persistent_volume_claim=k8s.V1PersistentVolumeClaimVolumeSource(
+                claim_name="pvc", read_only=True
+            ),
+        ),
+    ],
+    driver_volume_mounts=[
+        k8s.V1VolumeMount(name="volume1", mount_path="/mnt/volume1"),
+        k8s.V1VolumeMount(name="volume2", mount_path="/mnt/volume2", sub_path="sub-path"),
+        k8s.V1VolumeMount(name="volume3", mount_path="/mnt/volume3"),
+        k8s.V1VolumeMount(name="volume4", mount_path="/mnt/volume4"),
+        k8s.V1VolumeMount(name="volume5", mount_path="/mnt/volume5"),
+        k8s.V1VolumeMount(name="volume6", mount_path="/mnt/volume6"),
+        k8s.V1VolumeMount(name="volume7", mount_path="/mnt/volume7", read_only=True),
+    ],
+    
+)
+```
+
+#### Driver node selector
+Instead of providing `spark.kubernetes.driver.node.selector.[labelKey]=<labelValue>`, you can use:
+```python
+spark_client.submit_app(
+    ...,
+    driver_node_selector={"labelKey": "labelValue"},
+)
+```
+
+#### Driver tolerations
+Instead of configuring tolerations for the driver pod via a pod template file, you can use:
+```python
+from kubernetes import client as k8s
+
+spark_client.submit_app(
+    ...,
+    driver_tolerations=[
+        k8s.V1Toleration(
+            key="key1",
+            operator="Equal",
+            value="value1",
+            effect="NoSchedule",
+        ),
+        k8s.V1Toleration(
+            key="key2",
+            operator="Exists",
+            effect="NoExecute",
+        ),
+    ],
+)
+```
+
+#### Driver init containers
+Instead of adding init containers to the driver pod via a pod template file, you can use:
+```python
+from kubernetes import client as k8s
+
+spark_client.submit_app(
+    ...,
+    driver_init_containers=[
+        k8s.V1Container(
+            name="init-container1",
+            image="init-container1-image",
+            command=["init-command1"],
+            args=["init-arg1"],
+        ),
+        k8s.V1Container(
+            name="init-container2",
+            image="init-container2-image",
+            command=["init-command2"],
+            args=["init-arg2"],
+        ),
+    ],
+)
+```
+#### Driver host aliases
+Instead of providing host aliases (entries added to pod's /etc/hosts file) for the driver pod via a pod template file, you can use:
+```python
+from kubernetes import client as k8s
+
+spark_client.submit_app(
+    ...,
+    driver_host_aliases=[
+        k8s.V1HostAlias(
+            hostnames=["foo.local", "bar.local"],
+            ip="127.0.0.1",
+        )
+    ],
+)
+```