[SPARK-31234][SQL] ResetCommand should reset config to sc.conf only

### What changes were proposed in this pull request?
Currently, ResetCommand clear all configurations, including sql configs, static sql configs and spark context level configs.
for example:
```sql
spark-sql> set xyz=abc;
xyz abc
spark-sql> set;
spark.app.id local-1585055396930
spark.app.name SparkSQL::10.242.189.214
spark.driver.host 10.242.189.214
spark.driver.port 65094
spark.executor.id driver
spark.jars
spark.master local[*]
spark.sql.catalogImplementation hive
spark.sql.hive.version 1.2.1
spark.submit.deployMode client
xyz abc
spark-sql> reset;
spark-sql> set;
spark-sql> set spark.sql.hive.version;
spark.sql.hive.version 1.2.1
spark-sql> set spark.app.id;
spark.app.id <undefined>
```
In this PR, we restore spark confs to  RuntimeConfig after it is cleared

### Why are the changes needed?
reset command overkills configs which are static.
### Does this PR introduce any user-facing change?

yes, the ResetCommand do not change static configs now

### How was this patch tested?

add ut

Closes #28003 from yaooqinn/SPARK-31234.

Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

Author: yaooqinn

docs/sql-ref-syntax-aux-conf-mgmt-reset.md

@@ -20,7 +20,7 @@ license: |
 ---
 
 ### Description
-Reset all the properties specific to the current session to their default values. After RESET command, executing SET command will output empty.
+Reset any runtime configurations specific to the current session which were set via the [SET](sql-ref-syntax-aux-conf-mgmt-set.html) command to their default values.
 
 ### Syntax
 {% highlight sql %}
@@ -30,7 +30,7 @@ RESET
 
 ### Examples
 {% highlight sql %}
--- Reset all the properties specific to the current session to their default values.
+-- Reset any runtime configurations specific to the current session which were set via the SET command to their default values.
 RESET;
 {% endhighlight %}
 

sql/core/src/main/scala/org/apache/spark/sql/execution/command/SetCommand.scala

@@ -162,15 +162,20 @@ object SetCommand {
 }
 
 /**
- * This command is for resetting SQLConf to the default values. Command that runs
+ * This command is for resetting SQLConf to the default values. Any configurations that were set
+ * via [[SetCommand]] will get reset to default value. Command that runs
  * {{{
  *   reset;
  * }}}
  */
 case object ResetCommand extends RunnableCommand with IgnoreCachedData {
 
   override def run(sparkSession: SparkSession): Seq[Row] = {
-    sparkSession.sessionState.conf.clear()
+    val conf = sparkSession.sessionState.conf
+    conf.clear()
+    sparkSession.sparkContext.conf.getAll.foreach { case (k, v) =>
+      conf.setConfString(k, v)
+    }
     Seq.empty[Row]
   }
 }

sql/core/src/test/scala/org/apache/spark/sql/internal/SQLConfSuite.scala

@@ -116,6 +116,21 @@ class SQLConfSuite extends QueryTest with SharedSparkSession {
     }
   }
 
+  test("reset will not change static sql configs and spark core configs") {
+    val conf = spark.sparkContext.getConf.getAll.toMap
+    val appName = conf.get("spark.app.name")
+    val driverHost = conf.get("spark.driver.host")
+    val master = conf.get("spark.master")
+    val warehouseDir = conf.get("spark.sql.warehouse.dir")
+    // ensure the conf here is not default value, and will not be reset to default value later
+    assert(warehouseDir.get.contains(this.getClass.getCanonicalName))
+    sql("RESET")
+    assert(conf.get("spark.app.name") === appName)
+    assert(conf.get("spark.driver.host") === driverHost)
+    assert(conf.get("spark.master") === master)
+    assert(conf.get("spark.sql.warehouse.dir") === warehouseDir)
+  }
+
   test("reset - public conf") {
     spark.sessionState.conf.clear()
     val original = spark.conf.get(SQLConf.GROUP_BY_ORDINAL)