support swagger.enable (#902)

* support swagger.enable

* enable swagger by default

Co-authored-by: 璟源 <jingyuan.mj@alibaba-inc.com>
diff --git a/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/config/SwaggerConfiguration.java b/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/config/SwaggerConfiguration.java
index a4a4e8a..7f773a4 100644
--- a/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/config/SwaggerConfiguration.java
+++ b/dubbo-admin-server/src/main/java/org/apache/dubbo/admin/config/SwaggerConfiguration.java
@@ -17,6 +17,7 @@
 
 package org.apache.dubbo.admin.config;
 
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import springfox.documentation.builders.ApiInfoBuilder;
@@ -29,6 +30,7 @@
 
 @Configuration
 @EnableSwagger2
+@ConditionalOnProperty(name = "swagger.enable", havingValue = "true", matchIfMissing = true)
 public class SwaggerConfiguration {
     @Bean
     public Docket createRestApi() {