Add setter for autowired field in SpringWebSessionConfiguration

Closes gh-1918

Author: eleftherias

spring-session-core/src/main/java/org/springframework/session/config/annotation/web/server/SpringWebSessionConfiguration.java

@@ -38,12 +38,13 @@
 @Configuration(proxyBeanMethods = false)
 public class SpringWebSessionConfiguration {
 
-	/**
-	 * Optional override of default {@link WebSessionIdResolver}.
-	 */
-	@Autowired(required = false)
 	private WebSessionIdResolver webSessionIdResolver;
 
+	@Autowired(required = false)
+	public void setWebSessionIdResolver(WebSessionIdResolver webSessionIdResolver) {
+		this.webSessionIdResolver = webSessionIdResolver;
+	}
+
 	/**
 	 * Configure a {@link WebSessionManager} using a provided
 	 * {@link ReactiveSessionRepository}.