addTagHandler

@param identifier Handle handler unique Identifier, Used for subsequent Remove
```kotlin
NCEngine.addTagHandler("TAG_HANDLER_ID", object : TagHandler {
    override fun onTagChanged() {
        ========================================
        Tag.getTags { tags, error -> ... }
    }

    override fun onConversationTagChanged() {
        // 标签关联的频道发生变化
    }
})