Upgrade merge script to run on python3

It looks like the the parquet-java merge script is setup to run only on python2 which is EOL.  We should update it to run on python3 I plan to do this at least minimally without the Jira integration.

**Reporter**: [Micah Kornfield](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=emkornfield) / @emkornfield
**Assignee**: [Micah Kornfield](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=emkornfield) / @emkornfield
#### PRs and other links:
- [GitHub Pull Request #1373](https://github.com/apache/parquet-java/pull/1373)

_{**Note**: *This issue was originally created as [PARQUET-2495](https://issues.apache.org/jira/browse/PARQUET-2495). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

首先检查 parquet-java merge script 和链接的 GitHub pull request #1373。检查现有的 Python 2 假设和 issue 中说明的范围，然后验证该脚本在没有 Jira 集成的情况下能否在 Python 3 上运行。

由索引模型根据 Issue 内容生成。