chore: Add gRPC packages under extra-dependencies (#1640)

Add gRPC packages under extra-dependencies

Since gRPC in Python SDK is still under `_experimental` directory.
Keeping grpc packages under extra-dependencies.

These should be moved into mandatory dependencies once gRPC is out of
`_experimental` . See - b/465352227

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: chandra-siri

setup.py

@@ -43,6 +43,18 @@
     "google-crc32c >= 1.1.3, < 2.0.0",
 ]
 extras = {
+    # TODO: Make these extra dependencies as mandatory once gRPC out of
+    # experimental in this SDK. More info in b/465352227
+    "grpc": [
+        "google-api-core[grpc] >= 2.27.0, < 3.0.0",
+        "grpcio >= 1.33.2, < 2.0.0; python_version < '3.14'",
+        "grpcio >= 1.75.1, < 2.0.0; python_version >= '3.14'",
+        "grpcio-status >= 1.76.0, < 2.0.0",
+        "proto-plus >= 1.22.3, <2.0.0; python_version < '3.13'",
+        "proto-plus >= 1.25.0, <2.0.0; python_version >= '3.13'",
+        "protobuf>=3.20.2,<7.0.0,!=4.21.0,!=4.21.1,!=4.21.2,!=4.21.3,!=4.21.4,!=4.21.5",
+        "grpc-google-iam-v1 >= 0.14.0, <1.0.0",
+    ],
     "protobuf": ["protobuf >= 3.20.2, < 7.0.0"],
     "tracing": [
         "opentelemetry-api >= 1.1.0, < 2.0.0",