Add gRPC server sample with Spring Integration

basic/grpc-server/README.md

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+gRPC Server Sample
+==================
+
+This example demonstrates the use of **gRPC Inbound Gateway** with Spring Integration.
+
+It uses Java configuration and showcases various gRPC communication patterns including:
+
+* Unary RPC - client sends a single request and receives a single response
+* Server streaming RPC - client sends a single request and receives a stream of responses
+
+The sample uses a simple greeting service defined in a Protocol Buffers (protobuf) file that demonstrates how Spring Integration can handle gRPC service implementations through the `GrpcInboundGateway`.
+
+## Running the sample
+
+### Command Line Using Gradle
+
+To start the gRPC server application using Spring Boot run the following:
+
+    $ gradlew :grpc-server:bootRun
+
+To test the gRPC server application run the gRPC client sample using Spring Boot run as follows:
+
+    $ gradlew :grpc-client:bootRun
+
+You should see output that looks like the following:
+
+```log
+2026-03-25T11:10:18.538-04:00  INFO 91646 --- [           main] o.s.i.s.g.c.GrpcClientConfiguration      : Single response reply: Hello Jack
+2026-03-25T11:10:18.544-04:00  INFO 91646 --- [ault-executor-0] o.s.i.s.g.c.GrpcClientConfiguration      : Stream received reply: Hello Stream Jane
+2026-03-25T11:10:18.545-04:00  INFO 91646 --- [ault-executor-0] o.s.i.s.g.c.GrpcClientConfiguration      : Stream received reply: Hello again!
+```
+
+## Testing the sample
+
+The sample includes JUnit tests that demonstrate the various gRPC communication patterns:
+
+    $ gradlew :grpc-server:test
+
+### Output
+
+The tests use an in-process gRPC server for testing, configured via `spring.grpc.server.inprocess.name` and `spring.grpc.client.default-channel.address`. When running the unary test, a request with name "Jack" returns:
+
+    Hello Jack
+
+When running the server streaming test, a request with name "Jane" returns multiple responses:
+
+    Hello Stream Jane
+    Hello again!