[SPARK-22221][SQL][FOLLOWUP] Externalize spark.sql.execution.arrow.maxRecordsPerBatch

## What changes were proposed in this pull request?

This is a followup to #19575 which added a section on setting max Arrow record batches and this will externalize the conf that was referenced in the docs.

## How was this patch tested?
NA

Author: Bryan Cutler <cutlerb@gmail.com>

Closes #20423 from BryanCutler/arrow-user-doc-externalize-maxRecordsPerBatch-SPARK-22221.

(cherry picked from commit f235df6)
Signed-off-by: gatorsmile <gatorsmile@gmail.com>

Author: BryanCutler

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -1051,7 +1051,6 @@ object SQLConf {
 
   val ARROW_EXECUTION_MAX_RECORDS_PER_BATCH =
     buildConf("spark.sql.execution.arrow.maxRecordsPerBatch")
-      .internal()
       .doc("When using Apache Arrow, limit the maximum number of records that can be written " +
         "to a single ArrowRecordBatch in memory. If set to zero or negative there is no limit.")
       .intConf