[SPARK-47439][PYTHON] Document Python Data Source API in API referenc…

…e page

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

This PR proposes to document Python Data Source API in Python API reference page.

### Why are the changes needed?

For users/developers to know how to use them.

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

Yes, it documents Python Data Source API.

### How was this patch tested?

Manually checked the output from Python API reference build

```bash
cd python/docs
make clean html
open build/html/index.html
```

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

No.

Closes apache#45561 from HyukjinKwon/SPARK-47439.

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

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

@@ -42,3 +42,10 @@ Core Classes
     UDTFRegistration
     udf.UserDefinedFunction
     udtf.UserDefinedTableFunction
+    datasource.DataSource
+    datasource.DataSourceReader
+    datasource.DataSourceStreamReader
+    datasource.DataSourceWriter
+    datasource.DataSourceRegistration
+    datasource.InputPartition
+    datasource.WriterCommitMessage

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

@@ -0,0 +1,44 @@
+..  Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
+    distributed with this work for additional information
+    regarding copyright ownership.  The ASF licenses this file
+    to you under the Apache License, Version 2.0 (the
+    "License"); you may not use this file except in compliance
+    with the License.  You may obtain a copy of the License at
+
+..    http://www.apache.org/licenses/LICENSE-2.0
+
+..  Unless required by applicable law or agreed to in writing,
+    software distributed under the License is distributed on an
+    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+    KIND, either express or implied.  See the License for the
+    specific language governing permissions and limitations
+    under the License.
+
+
+==================
+Python Data Source
+==================
+
+.. currentmodule:: pyspark.sql.datasource
+
+.. autosummary::
+    :toctree: api/
+
+    DataSource.name
+    DataSource.reader
+    DataSource.schema
+    DataSource.streamReader
+    DataSource.writer
+    DataSourceReader.partitions
+    DataSourceReader.read
+    DataSourceRegistration.register
+    DataSourceStreamReader.commit
+    DataSourceStreamReader.initialOffset
+    DataSourceStreamReader.latestOffset
+    DataSourceStreamReader.partitions
+    DataSourceStreamReader.read
+    DataSourceStreamReader.stop
+    DataSourceWriter.abort
+    DataSourceWriter.commit
+    DataSourceWriter.write

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

@@ -42,3 +42,4 @@ This page gives an overview of all public Spark SQL API.
     udf
     udtf
     protobuf
+    datasource

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

@@ -47,6 +47,7 @@ See also :class:`SparkSession`.
     SparkSession.catalog
     SparkSession.conf
     SparkSession.createDataFrame
+    SparkSession.dataSource
     SparkSession.getActiveSession
     SparkSession.newSession
     SparkSession.profile