feature：增加obs归集方式 (#90)

* feature：实现通过datax进行obs归集的插件

* feature：前端增加obs归集时的前缀参数

runtime/datax/obswriter/src/main/resources/plugin.json

@@ -0,0 +1,6 @@
+{
+  "name": "obswriter",
+  "class": "com.datamate.plugin.writer.obswriter.ObsWriter",
+  "description": "writer obs file to local",
+  "developer": "datamate"
+}

runtime/datax/obswriter/src/main/resources/plugin_job_template.json

@@ -0,0 +1,11 @@
+{
+  "name": "obswriter",
+  "parameter": {
+    "endpoint": "127.0.0.1",
+    "bucket": "test",
+    "accessKey": "ak-xxx",
+    "secretKey": "sk-xxx",
+    "prefix": "/test",
+    "destPath": "/test"
+  }
+}