refactor dubbo examples & add datasource feature in example & update docs

spring-cloud-alibaba-examples/sentinel-dubbo-provider-example/src/main/java/org/springframework/cloud/alibaba/cloud/examples/FooServiceImpl.java

@@ -0,0 +1,20 @@
+package org.springframework.cloud.alibaba.cloud.examples;
+
+import com.alibaba.dubbo.config.annotation.Service;
+
+/**
+ * @author fangjian
+ */
+@Service(
+        version = "${foo.service.version}",
+        application = "${dubbo.application.id}",
+        protocol = "${dubbo.protocol.id}",
+        registry = "${dubbo.registry.id}"
+)
+public class FooServiceImpl implements FooService {
+
+    @Override
+    public String hello(String name) {
+        return "hello, " + name;
+    }
+}

spring-cloud-alibaba-examples/sentinel-dubbo-provider-example/src/main/java/org/springframework/cloud/alibaba/cloud/examples/SentinelDubboProviderApp.java

@@ -0,0 +1,19 @@
+package org.springframework.cloud.alibaba.cloud.examples;
+
+import org.springframework.boot.WebApplicationType;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.builder.SpringApplicationBuilder;
+
+/**
+ * @author fangjian
+ */
+@SpringBootApplication
+public class SentinelDubboProviderApp {
+
+	public static void main(String[] args) {
+		SpringApplicationBuilder providerBuilder = new SpringApplicationBuilder();
+		providerBuilder.web(WebApplicationType.NONE)
+				.sources(SentinelDubboProviderApp.class).run(args);
+	}
+
+}

spring-cloud-alibaba-examples/sentinel-dubbo-provider-example/src/main/resources/application.properties

@@ -0,0 +1,16 @@
+spring.application.name = dubbo-provider-demo
+
+foo.service.version = 1.0.0
+
+dubbo.scan.basePackages = org.springframework.cloud.alibaba.cloud.examples
+
+dubbo.application.id = dubbo-provider-demo
+dubbo.application.name = dubbo-provider-demo
+
+dubbo.protocol.id = dubbo
+dubbo.protocol.name = dubbo
+dubbo.protocol.port = 12345
+dubbo.protocol.status = server
+
+dubbo.registry.id = my-registry
+dubbo.registry.address = N/A