[ONOS-3648] Implement REST API for collecting system metrics

- Implement REST API for gathering system metrics
- Add unit test for REST API
- Add swagger doc for REST API

Change-Id: Iedd21a5f6ed14d595e4d35c1fa08270b48a5031e
diff --git a/apps/cpman/src/main/resources/definitions/DiskMetricsPost.json b/apps/cpman/src/main/resources/definitions/DiskMetricsPost.json
new file mode 100644
index 0000000..fe0dab1
--- /dev/null
+++ b/apps/cpman/src/main/resources/definitions/DiskMetricsPost.json
@@ -0,0 +1,19 @@
+{
+  "type": "object",
+  "required": [
+    "readBytes",
+    "writeBytes"
+  ],
+  "properties": {
+    "readBytes": {
+      "type": "integer",
+      "format": "int64",
+      "example": "500"
+    },
+    "writeBytes": {
+      "type": "integer",
+      "format": "int64",
+      "example": "300"
+    }
+  }
+}
\ No newline at end of file