[SPARK-47762][PYTHON][CONNECT] Add pyspark.sql.connect.protobuf into setup.py

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

This PR is a followup of #42563 (but using new JIRA as it's already released), which adds `pyspark.sql.connect.protobuf` into `setup.py`.

### Why are the changes needed?

So PyPI packaged PySpark can support protobuf function with Spark Connect on.

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

Yes. The new feature is now available with Spark Connect on if users install Spark Connect by `pip`.

### How was this patch tested?

Being tested in #45870

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

No.

Closes #45924 from HyukjinKwon/SPARK-47762.

Authored-by: Hyukjin Kwon <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: HyukjinKwon

python/packaging/classic/setup.py

@@ -275,6 +275,7 @@ def run(self):
             "pyspark.sql.connect.client",
             "pyspark.sql.connect.functions",
             "pyspark.sql.connect.proto",
+            "pyspark.sql.connect.protobuf",
             "pyspark.sql.connect.shell",
             "pyspark.sql.connect.streaming",
             "pyspark.sql.connect.streaming.worker",

python/packaging/connect/setup.py

@@ -103,6 +103,7 @@
         "pyspark.sql.connect.client",
         "pyspark.sql.connect.functions",
         "pyspark.sql.connect.proto",
+        "pyspark.sql.connect.protobuf",
         "pyspark.sql.connect.shell",
         "pyspark.sql.connect.streaming",
         "pyspark.sql.connect.streaming.worker",