feat: add FlowCanvas (#593)

### What problem does this PR solve?

feat: handle operator drag
feat: add FlowCanvas
#592

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

web/src/pages/flow/mock.tsx

@@ -0,0 +1,11 @@
+import {
+  MergeCellsOutlined,
+  RocketOutlined,
+  SendOutlined,
+} from '@ant-design/icons';
+
+export const componentList = [
+  { name: 'Begin', icon: <SendOutlined />, description: '' },
+  { name: 'Retrieval', icon: <RocketOutlined />, description: '' },
+  { name: 'Generate', icon: <MergeCellsOutlined />, description: '' },
+];