What is the analogue to CKSyncEngine for public databases

还没有人认领这个 Issue。

I modified this piece:

```
func initializeSyncEngine() {
var configuration = CKSyncEngine.Configuration(
database: Self.container.publicCloudDatabase, // <<<<<<<<<<<<<<<<<<<<< THIS
stateSerialization: self.appData.stateSerialization,
delegate: self
)
```
And hit the error:

```
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'CKSyncEngine cannot be used in the Public database'
*** First throw call stack:
```

So I read (quickly 😄 ) the documentation and noticed this tid-bit:

So, basically my question is , what is the alternative to `CKSyncEngine` providing the easiest way to sync a local database with the remote public iCloud?

从 issue 中展示的 initializeSyncEngine 函数和 CKSyncEngine.Configuration 设置开始，然后查阅 Apple 的 CloudKit 文档，了解对公共数据库的支持。确定一种受支持的方法，用于将本地数据库与公共数据库同步；当该方法及其限制得到记录时，工作即完成。

由索引模型根据 Issue 内容生成。