[SPARK-26700][CORE][FOLLOWUP] Add config spark.network.maxRemoteBlockSizeFetchToMem

### What changes were proposed in this pull request?
Add new config `spark.network.maxRemoteBlockSizeFetchToMem` fallback to the old config `spark.maxRemoteBlockSizeFetchToMem`.

### Why are the changes needed?
For naming consistency.

### Does this PR introduce any user-facing change?
No.

### How was this patch tested?
Existing tests.

Closes #27463 from xuanyuanking/SPARK-26700-follow.

Authored-by: Yuanjian Li <xyliyuanjian@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

Author: xuanyuanking

core/src/main/scala/org/apache/spark/SparkConf.scala

@@ -684,7 +684,8 @@ private[spark] object SparkConf extends Logging {
     "spark.yarn.jars" -> Seq(
       AlternateConfig("spark.yarn.jar", "2.0")),
     MAX_REMOTE_BLOCK_SIZE_FETCH_TO_MEM.key -> Seq(
-      AlternateConfig("spark.reducer.maxReqSizeShuffleToMem", "2.3")),
+      AlternateConfig("spark.reducer.maxReqSizeShuffleToMem", "2.3"),
+      AlternateConfig("spark.maxRemoteBlockSizeFetchToMem", "3.0")),
     LISTENER_BUS_EVENT_QUEUE_CAPACITY.key -> Seq(
       AlternateConfig("spark.scheduler.listenerbus.eventqueue.size", "2.3")),
     DRIVER_MEMORY_OVERHEAD.key -> Seq(

core/src/main/scala/org/apache/spark/internal/config/package.scala

@@ -895,7 +895,7 @@ package object config {
       .createWithDefault(Int.MaxValue)
 
   private[spark] val MAX_REMOTE_BLOCK_SIZE_FETCH_TO_MEM =
-    ConfigBuilder("spark.maxRemoteBlockSizeFetchToMem")
+    ConfigBuilder("spark.network.maxRemoteBlockSizeFetchToMem")
       .doc("Remote block will be fetched to disk when size of the block is above this threshold " +
         "in bytes. This is to avoid a giant request takes too much memory. Note this " +
         "configuration will affect both shuffle fetch and block manager remote block fetch. " +

docs/configuration.md

@@ -1810,7 +1810,7 @@ Apart from these, the following properties are also available, and may be useful
   </td>
 </tr>
 <tr>
-  <td><code>spark.maxRemoteBlockSizeFetchToMem</code></td>
+  <td><code>spark.network.maxRemoteBlockSizeFetchToMem</code></td>
   <td>200m</td>
   <td>
     Remote block will be fetched to disk when size of the block is above this threshold