Generate metadata for config props

Adds the `spring-boot-configuration-processor` to enable automatic metadata
generation so our config props play well in IDEs.

Also updates the default values for duration properties to use
`Duration.of<Unit>(long)` instead of `Duration.of(long, DurationUnit)` as
Spring Boot config processor can not determine a default for the config
metadata in the latter format.

Author: onobc

spring-grpc-spring-boot-autoconfigure/pom.xml

@@ -22,6 +22,12 @@
 
 	<dependencies>
 
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-configuration-processor</artifactId>
+			<optional>true</optional>
+		</dependency>
+
 		<dependency>
 			<groupId>com.google.protobuf</groupId>
 			<artifactId>protobuf-java</artifactId>

spring-grpc-spring-boot-autoconfigure/src/main/java/org/springframework/grpc/autoconfigure/server/GrpcServerProperties.java

@@ -49,13 +49,13 @@ public class GrpcServerProperties {
 	 * shutdown immediately. The default is 30 seconds.
 	 */
 	@DurationUnit(ChronoUnit.SECONDS)
-	private Duration shutdownGracePeriod = Duration.of(30, ChronoUnit.SECONDS);
+	private Duration shutdownGracePeriod = Duration.ofSeconds(30);
 
 	/**
 	 * Maximum message size allowed to be received by the server (default 4MiB).
 	 */
 	@DataSizeUnit(DataUnit.BYTES)
-	private DataSize maxInboundMessageSize = DataSize.ofBytes(4 * 1024 * 1024);
+	private DataSize maxInboundMessageSize = DataSize.ofBytes(4194304);
 
 	/**
 	 * Maximum metadata size allowed to be received by the server (default 8KiB).
@@ -115,15 +115,15 @@ public static class KeepAlive {
 		 * Duration without read activity before sending a keep alive ping (default 2h).
 		 */
 		@DurationUnit(ChronoUnit.SECONDS)
-		private Duration time = Duration.of(2, ChronoUnit.HOURS);
+		private Duration time = Duration.ofHours(2);
 
 		/**
 		 * Maximum time to wait for read activity after sending a keep alive ping. If
 		 * sender does not receive an acknowledgment within this time, it will close the
 		 * connection (default 20s).
 		 */
 		@DurationUnit(ChronoUnit.SECONDS)
-		private Duration timeout = Duration.of(20, ChronoUnit.SECONDS);
+		private Duration timeout = Duration.ofSeconds(20);
 
 		/**
 		 * Maximum time a connection can remain idle before being gracefully terminated
@@ -149,7 +149,7 @@ public static class KeepAlive {
 		 * Maximum keep-alive time clients are permitted to configure (default 5m).
 		 */
 		@DurationUnit(ChronoUnit.SECONDS)
-		private Duration permitTime = Duration.of(5, ChronoUnit.MINUTES);
+		private Duration permitTime = Duration.ofMinutes(5);
 
 		/**
 		 * Whether clients are permitted to send keep alive pings when there are no