[SPARK-44481][CONNECT][PYTHON] Make pyspark.sql.is_remote an API

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

This PR proposes to expose and document `pyspark.sql.is_remote` as an API.

### Why are the changes needed?

For the end users to be able to do if-else, e.g., for dispatching the code path to the legacy mode or connect mode.

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

Yes, it exposes a method as an API.

### How was this patch tested?

Manually built and checked the documentation.

Closes #42072 from HyukjinKwon/SPARK-44481.

Authored-by: Hyukjin Kwon <gurwls223@apache.org>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

Author: HyukjinKwon

python/docs/source/reference/pyspark.sql/spark_session.rst

@@ -50,7 +50,7 @@ See also :class:`SparkSession`.
     SparkSession.udf
     SparkSession.udtf
     SparkSession.version
-
+    is_remote
 
 Spark Connect Only
 ------------------

python/pyspark/sql/__init__.py

@@ -50,6 +50,7 @@
 from pyspark.sql.readwriter import DataFrameReader, DataFrameWriter, DataFrameWriterV2
 from pyspark.sql.window import Window, WindowSpec
 from pyspark.sql.pandas.group_ops import PandasCogroupedOps
+from pyspark.sql.utils import is_remote
 
 
 __all__ = [
@@ -72,4 +73,5 @@
     "DataFrameWriter",
     "DataFrameWriterV2",
     "PandasCogroupedOps",
+    "is_remote",
 ]

python/pyspark/sql/utils.py

@@ -146,6 +146,25 @@ def is_timestamp_ntz_preferred() -> bool:
 def is_remote() -> bool:
     """
     Returns if the current running environment is for Spark Connect.
+
+    .. versionadded:: 4.0.0
+
+    Notes
+    -----
+    This will only return ``True`` if there is a remote session running.
+    Otherwise, it returns ``False``.
+
+    This API is unstable, and for developers.
+
+    Returns
+    -------
+    bool
+
+    Examples
+    --------
+    >>> from pyspark.sql import is_remote
+    >>> is_remote()
+    False
     """
     return "SPARK_CONNECT_MODE_ENABLED" in os.environ