Add format plugin to samples

This adds the spring-javaformat plugin to the samples
module. The motivation is as follows:

- Keep the samples in the Spring recommended format
- Allow running `./mvnw spring-javaformat:apply` at project root

samples/grpc-server/pom.xml

@@ -31,6 +31,7 @@
 		<java.version>17</java.version>
 		<protobuf-java.version>3.25.2</protobuf-java.version>
 		<grpc.version>1.63.0</grpc.version>
+		<spring-javaformat-maven-plugin.version>0.0.39</spring-javaformat-maven-plugin.version>
 	</properties>
 	<dependencies>
 		<dependency>
@@ -79,6 +80,20 @@
 					<skip>true</skip>
 				</configuration>
 			</plugin>
+			<plugin>
+				<groupId>io.spring.javaformat</groupId>
+				<artifactId>spring-javaformat-maven-plugin</artifactId>
+				<version>${spring-javaformat-maven-plugin.version}</version>
+				<executions>
+					<execution>
+						<phase>validate</phase>
+						<inherited>true</inherited>
+						<goals>
+							<goal>validate</goal>
+						</goals>
+					</execution>
+				</executions>
+			</plugin>
 			<plugin>
 				<groupId>org.xolstice.maven.plugins</groupId>
 				<artifactId>protobuf-maven-plugin</artifactId>
@@ -102,4 +117,4 @@
 		</plugins>
 	</build>
 
-</project>
+</project>