Update docs to include SASL support for RPC

## What changes were proposed in this pull request?

Update docs to include SASL support for RPC

Evidence: https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/rpc/netty/NettyRpcEnv.scala#L63

## How was this patch tested?

Docs change only

Author: Michael Gummelt <[email protected]>

Closes #14549 from mgummelt/sasl.

Author: Michael Gummelt

docs/configuration.md

@@ -1211,7 +1211,7 @@ Apart from these, the following properties are also available, and may be useful
   <td>false</td>
   <td>
     Whether to use dynamic resource allocation, which scales the number of executors registered
-    with this application up and down based on the workload. 
+    with this application up and down based on the workload.
     For more detail, see the description
     <a href="job-scheduling.html#dynamic-resource-allocation">here</a>.
     <br><br>
@@ -1352,8 +1352,9 @@ Apart from these, the following properties are also available, and may be useful
   <td><code>spark.authenticate.enableSaslEncryption</code></td>
   <td>false</td>
   <td>
-    Enable encrypted communication when authentication is enabled. This option is currently
-    only supported by the block transfer service.
+    Enable encrypted communication when authentication is
+    enabled. This is supported by the block transfer service and the
+    RPC endpoints.
   </td>
 </tr>
 <tr>

docs/security.md

@@ -27,7 +27,8 @@ If your applications are using event logging, the directory where the event logs
 
 ## Encryption
 
-Spark supports SSL for HTTP protocols. SASL encryption is supported for the block transfer service.
+Spark supports SSL for HTTP protocols. SASL encryption is supported for the block transfer service
+and the RPC endpoints.
 
 Encryption is not yet supported for data stored by Spark in temporary local storage, such as shuffle
 files, cached data, and other application files. If encrypting this data is desired, a workaround is