[SPARK-46095][DOCS] Document REST API for Spark Standalone Cluster

This PR aims to document `REST API` for Spark Standalone Cluster.

To help the users to understand Apache Spark features.

No.

Manual review. `REST API` Section is added newly.

**AFTER**

<img width="704" alt="Screenshot 2023-11-24 at 4 13 53 PM" src="https://github.com/apache/spark/assets/9700541/a4e09d94-d216-4629-8b37-9d350365a428">

No.

Closes apache#44007 from dongjoon-hyun/SPARK-46095.

Authored-by: Dongjoon Hyun <dhyun@apple.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>
(cherry picked from commit 132c1a1)
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

docs/spark-standalone.md

@@ -444,6 +444,8 @@ Spark applications supports the following configuration properties specific to s
 
 # Launching Spark Applications
 
+## Spark Protocol
+
 The [`spark-submit` script](submitting-applications.html) provides the most straightforward way to
 submit a compiled Spark application to the cluster. For standalone clusters, Spark currently
 supports two deploy modes. In `client` mode, the driver is launched in the same process as the
@@ -466,6 +468,72 @@ failing repeatedly, you may do so through:
 
 You can find the driver ID through the standalone Master web UI at `http://<master url>:8080`.
 
+## REST API
+
+If `spark.master.rest.enabled` is enabled, Spark master provides additional REST API
+via <code>http://[host:port]/[version]/submissions/[action]</code> where
+<code>host</code> is the master host, and
+<code>port</code> is the port number specified by `spark.master.rest.port` (default: 6066), and 
+<code>version</code> is a protocol version, <code>v1</code> as of today, and
+<code>action</code> is one of the following supported actions.
+
+<table class="table table-striped">
+  <thead><tr><th style="width:21%">Command</th><th>Description</th><th>HTTP METHOD</th><th>Since Version</th></tr></thead>
+  <tr>
+    <td><code>create</code></td>
+    <td>Create a Spark driver via <code>cluster</code> mode.</td>
+    <td>POST</td>
+    <td>1.3.0</td>
+  </tr>
+  <tr>
+    <td><code>kill</code></td>
+    <td>Kill a single Spark driver.</td>
+    <td>POST</td>
+    <td>1.3.0</td>
+  </tr>
+  <tr>
+    <td><code>status</code></td>
+    <td>Check the status of a Spark job.</td>
+    <td>GET</td>
+    <td>1.3.0</td>
+  </tr>
+</table>
+
+The following is a <code>curl</code> CLI command example with the `pi.py` and REST API.
+
+```bash
+$ curl -XPOST http://IP:PORT/v1/submissions/create \
+--header "Content-Type:application/json;charset=UTF-8" \
+--data '{
+  "appResource": "",
+  "sparkProperties": {
+    "spark.master": "spark://master:7077",
+    "spark.app.name": "Spark Pi",
+    "spark.driver.memory": "1g",
+    "spark.driver.cores": "1",
+    "spark.jars": ""
+  },
+  "clientSparkVersion": "",
+  "mainClass": "org.apache.spark.deploy.SparkSubmit",
+  "environmentVariables": { },
+  "action": "CreateSubmissionRequest",
+  "appArgs": [ "/opt/spark/examples/src/main/python/pi.py", "10" ]
+}'
+```
+
+The following is the response from the REST API for the above <code>create</code> request.
+
+```bash
+{
+  "action" : "CreateSubmissionResponse",
+  "message" : "Driver successfully submitted as driver-20231124153531-0000",
+  "serverSparkVersion" : "3.4.2",
+  "submissionId" : "driver-20231124153531-0000",
+  "success" : true
+}
+```
+
+
 # Resource Scheduling
 
 The standalone cluster mode currently only supports a simple FIFO scheduler across applications.