add user crud interface in impl

internal/user/store.go

@@ -0,0 +1,9 @@
+package user
+
+type UserCRUD interface {
+	Create(user *User) error
+	GetByID(id int64) (*User, error)
+	GetByUsername(username string) (*User, error)
+	Update(user *User) error
+	Delete(id int64) error
+}