sync code with dubbo version in 1.x

spring-cloud-alibaba-sentinel/pom.xml

@@ -33,6 +33,13 @@
         <dependency>
             <groupId>com.alibaba.csp</groupId>
             <artifactId>sentinel-dubbo-adapter</artifactId>
+            <optional>true</optional>
+        </dependency>
+
+        <dependency>
+            <groupId>com.alibaba.csp</groupId>
+            <artifactId>sentinel-apache-dubbo-adapter</artifactId>
+            <optional>true</optional>
         </dependency>
 
         <dependency>

spring-cloud-alibaba-sentinel/src/main/java/org/springframework/cloud/alibaba/sentinel/custom/SentinelAutoConfiguration.java

@@ -178,6 +178,7 @@ public class SentinelAutoConfiguration {
 		return new SentinelDataSourceHandler(beanFactory);
 	}
 
+	@ConditionalOnClass(ObjectMapper.class)
 	protected static class SentinelConverterConfiguration {
 
 		private ObjectMapper objectMapper = new ObjectMapper();