增加扩展设置元数据的功能

discovery-springcloud-example-service/src/main/java/com/nepxion/discovery/plugin/example/service/context/MyApplicationContextInitializer.java

+package com.nepxion.discovery.plugin.example.service.context;
+
+import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
+import org.springframework.context.ApplicationContextInitializer;
+import org.springframework.context.ConfigurableApplicationContext;
+
+// 通过如下方式，可以代替在配置文件里面配置元数据，格式为ext.xxx。例如，如果version希望通过git插件获取到最后一次提交编号，可以动态在这里进行解析并放入
+public class MyApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
+    @Override
+    public void initialize(ConfigurableApplicationContext applicationContext) {
+        if (applicationContext instanceof AnnotationConfigServletWebServerApplicationContext) {
+            // System.setProperty("ext.group", "myGroup");
+            // System.setProperty("ext.version", "8888");
+            // System.setProperty("ext.region", "myRegion");
+        }
+    }
+}
\ No newline at end of file

discovery-springcloud-example-service/src/main/resources/META-INF/spring.factories

+org.springframework.context.ApplicationContextInitializer=\
+com.nepxion.discovery.plugin.example.service.context.MyApplicationContextInitializer
\ No newline at end of file