Add service API handler stubs for status, stop and restart (#3417)

docs/admin-api/service.md

@@ -0,0 +1,33 @@
+# Service REST API
+
+## Authentication
+- AWS signatureV4
+- We use "minio" as region. Here region is set only for signature calculation.
+
+## List of management APIs
+- Service
+  - Stop
+  - Restart
+  - Status
+
+- Locks
+  - List
+  - Clear
+
+- Healing
+
+### Service Management APIs
+* Stop
+  - POST /?service
+  - x-minio-operation: stop
+  - Response: On success 200
+
+* Restart
+  - POST /?service
+  - x-minio-operation: restart
+  - Response: On success 200
+
+* Status
+  - GET /?service
+  - x-minio-operation: status
+  - Response: On success 200, return json formatted StorageInfo object.