Add auto-configuration for Jetty’s GzipFilter

Jetty’s GzipFilter is a container-agnostic Filter that can be used to
provide gzip and deflate encoding of HTTP responses. This commit adds
auto-configuration for GzipFilter that is enabled when
org.eclipse.jetty:jetty-servlets is on the classpath. The filter can
be configured using spring.http.gzip.*

See gh-2031

spring-boot-dependencies/pom.xml

@@ -983,6 +983,11 @@
 				<artifactId>jetty-security</artifactId>
 				<version>${jetty.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.eclipse.jetty</groupId>
+				<artifactId>jetty-server</artifactId>
+				<version>${jetty.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.eclipse.jetty</groupId>
 				<artifactId>jetty-servlet</artifactId>
@@ -990,7 +995,7 @@
 			</dependency>
 			<dependency>
 				<groupId>org.eclipse.jetty</groupId>
-				<artifactId>jetty-server</artifactId>
+				<artifactId>jetty-servlets</artifactId>
 				<version>${jetty.version}</version>
 			</dependency>
 			<dependency>