review gradle wrapper usage

The ASF don't think including gradle-wrapper jars in source releases is a good idea.

https://issues.apache.org/jira/browse/LEGAL-570

* we could remove the gradle wrapper and fix docs to say that the user needs to install gradle themselves if they want to use gradle
* we could try to hack the gradlew scripts to fetch the gradle-wrapper jar but this is harder with Windows (Linux/Mac users can be more readily expected to have wget or curl available)
* we don't release this repo - so we might not be required to get rid of the gradle-wrapper jar

首先阅读链接的 LEGAL-570 讨论，并检查 gradle-wrapper jars、gradlew scripts 以及仓库提到的任何文档。确定列出的哪种方法是此仓库所需的，然后确认所选的 wrapper 或安装指南满足受支持平台上的 release policy。

由索引模型根据 Issue 内容生成。