feat: Add Checkin (#719)

* feat: Add Checkin

- Implement 'getcheckindata' API

* refactor: Change variable names

* refactor: Change struct name

work/checkin/client.go

@@ -0,0 +1,17 @@
+package checkin
+
+import (
+	"github.com/silenceper/wechat/v2/work/context"
+)
+
+// Client 打卡接口实例
+type Client struct {
+	*context.Context
+}
+
+// NewClient 初始化实例
+func NewClient(ctx *context.Context) *Client {
+	return &Client{
+		ctx,
+	}
+}