[MINOR][SS][DOCS] Point to correct examples of Arbitrary Stateful Operations
[MINOR][SS][DOCS] Point to correct examples of Arbitrary Stateful Operations

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

This fixes incorrect example links in Structured Streaming Programming Guide.

### Why are the changes needed?

StructuredSessionization.scala and JavaStructuredSessionization.java are now using session window expression, not `flatMapGroupsWithState`. The section talks about arbitrary stateful operations and should point to another examples.

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

No

### How was this patch tested?

Doc change only.

Closes #34408 from viirya/fix-ss-doc.

Authored-by: Liang-Chi Hsieh <d24118b4297e1ecf0c990d6935f5f9e6e4fd7701@gmail.com>
Signed-off-by: Liang-Chi Hsieh <d24118b4297e1ecf0c990d6935f5f9e6e4fd7701@gmail.com>
(cherry picked from commit 5b2bbcef6854c495c32b37e383dd5f1f6ce23dd4)
Signed-off-by: Liang-Chi Hsieh <d24118b4297e1ecf0c990d6935f5f9e6e4fd7701@gmail.com>

milliman/spark,milliman/spark,milliman/spark,milliman/spark,milliman/spark,milliman/spark,milliman/spark