[SPARK-50251][PYTHON] Add getSystemProperty to PySpark SparkContext

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

This PR aims to add `getSystemProperty` to PySpark `SparkContext` like `setSystemProperty` at Apache Spark 4.0.0.

https://spark.apache.org/docs/4.0.0-preview2/api/python/reference/api/pyspark.SparkContext.setSystemProperty.html

### Why are the changes needed?

Since Apache Spark 0.9.0, `setSystemProperty` has been provided because Python doesn't have JVM's `SystemProperties` concept. This is usefully used like the following.

https://github.com/apache/spark/blob/99d27c9701019a0f534cc13c084895a00badee12/python/pyspark/shell.py#L84

This PR aims to add `getSystemProperty` additionally and symmetrically to provide an easier and better experience for both Spark developers and Spark App developers.

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

No. This is a new API.

### How was this patch tested?

Pass the CIs with newly added doctests.

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

No.

Closes apache#48781 from dongjoon-hyun/SPARK-50251.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

python/docs/source/reference/pyspark.rst

@@ -74,6 +74,7 @@ Spark Context APIs
     SparkContext.getJobTags
     SparkContext.getLocalProperty
     SparkContext.getOrCreate
+    SparkContext.getSystemProperty
     SparkContext.hadoopFile
     SparkContext.hadoopRDD
     SparkContext.listArchives

python/pyspark/core/context.py

@@ -554,6 +554,28 @@ def setSystemProperty(cls, key: str, value: str) -> None:
         assert SparkContext._jvm is not None
         SparkContext._jvm.java.lang.System.setProperty(key, value)
 
+    @classmethod
+    def getSystemProperty(cls, key: str) -> str:
+        """
+        Get a Java system property, such as `java.home`.
+
+        .. versionadded:: 4.0.0
+
+        Parameters
+        ----------
+        key : str
+            The key of a new Java system property.
+
+        Examples
+        --------
+        >>> sc.getSystemProperty("SPARK_SUBMIT")
+        'true'
+        >>> _ = sc.getSystemProperty("java.home")
+        """
+        SparkContext._ensure_initialized()
+        assert SparkContext._jvm is not None
+        return SparkContext._jvm.java.lang.System.getProperty(key)
+
     @property
     def version(self) -> str:
         """