[Docs] Kuberay Sidecar Mode (#58273)

Signed-off-by: Future-Outlier <[email protected]>
Signed-off-by: Han-Ju Chen (Future-Outlier) <[email protected]>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: Future-Outlier

doc/source/cluster/kubernetes/getting-started/rayjob-quick-start.md

@@ -54,6 +54,7 @@ To understand the following content better, you should understand the difference
     * `K8sJobMode`: The KubeRay operator creates a submitter Kubernetes Job to submit the Ray job.
     * `HTTPMode`: The KubeRay operator sends a request to the RayCluster to create a Ray job.
     * `InteractiveMode`: The KubeRay operator waits for the user to submit a job to the RayCluster. This mode is currently in alpha and the [KubeRay kubectl plugin](kubectl-plugin) relies on it.
+    * `SidecarMode`: The KubeRay operator injects a container into the Ray head Pod to submit the Ray job. This mode does not support `clusterSelector`, `submitterPodTemplate`, and `submitterConfig`, and requires the head Pod's restart policy to be `Never`.
   * `submitterPodTemplate` (Optional): Defines the Pod template for the submitter Kubernetes Job. This field is only effective when `submissionMode` is "K8sJobMode".
     * `RAY_DASHBOARD_ADDRESS` - The KubeRay operator injects this environment variable to the submitter Pod. The value is `$HEAD_SERVICE:$DASHBOARD_PORT`.
     * `RAY_JOB_SUBMISSION_ID` - The KubeRay operator injects this environment variable to the submitter Pod. The value is the `RayJob.Status.JobId` of the RayJob.