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.*}

Beginne mit der Überprüfung des parquet-java merge script und des verlinkten GitHub pull request #1373. Prüfe die bestehenden Python 2-Annahmen und den im Issue angegebenen Umfang. Verifiziere anschließend, dass das Script unter Python 3 ohne die Jira-Integration ausgeführt werden kann.

Vom Indexierungsmodell aus dem Issue-Text verfasst.