[SPARK-49249][SQL][FOLLOWUP] Rename spark.sql.artifact.isolation.(always.apply.classloader -> alwaysApplyClassloader)

### What changes were proposed in this pull request?

This is a follow-up to rename a new configuration to comply Apache Spark config namespace.
- #48120

### Why are the changes needed?

Currently, `spark.sql.artifact.isolation.always.apply.classloader` config name introduces redundant namespace `spark.sql.artifact.isolation.always.*` and `spark.sql.artifact.isolation.always.apply.*`.
```
- spark.sql.artifact.isolation.always.apply.classloader
+ spark.sql.artifact.isolation.alwaysApplyClassloader
```

Since we have `spark.sql.artifact.isolation.enabled` already, we had better keep the above in the same namespace `spark.sql.artifact.isolation.*`.

### Does this PR introduce _any_ user-facing change?

No, this is a newly added configuration at Spark 4.0.0

### How was this patch tested?

Pass the CIs.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #49101 from dongjoon-hyun/SPARK-49249.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: yangjie01 <[email protected]>

Author: dongjoon-hyun

python/pyspark/sql/connect/session.py

@@ -1044,7 +1044,7 @@ def _start_connect_server(master: str, opts: Dict[str, Any]) -> None:
             default_conf = {
                 "spark.plugins": "org.apache.spark.sql.connect.SparkConnectPlugin",
                 "spark.sql.artifact.isolation.enabled": "true",
-                "spark.sql.artifact.isolation.always.apply.classloader": "true",
+                "spark.sql.artifact.isolation.alwaysApplyClassloader": "true",
             }
 
             if "SPARK_TESTING" in os.environ:

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

@@ -3999,7 +3999,7 @@ object SQLConf {
       .createWithDefault(true)
 
   val ARTIFACTS_SESSION_ISOLATION_ALWAYS_APPLY_CLASSLOADER =
-    buildConf("spark.sql.artifact.isolation.always.apply.classloader")
+    buildConf("spark.sql.artifact.isolation.alwaysApplyClassloader")
       .internal()
       .doc("When enabled, the classloader holding per-session artifacts will always be applied " +
         "during SQL executions (useful for Spark Connect). When disabled, the classloader will " +