C++: Check in release that the correct author is set in git

We should check if the correct author to sign the release tarball is set as the git author. Not sure how we can detect that but I already run twice into the problem that the git author was not the same as I signed the tarball with and the release script aborted half-way. This was not catched in the dry-run mode.

**Reporter**: [Uwe Korn](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=uwe) / @xhochy

_{**Note**: *This issue was originally created as [PARQUET-912](https://issues.apache.org/jira/browse/PARQUET-912). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Beginne damit, das Release-Skript zu finden und seine normalen und Dry-Run-Pfade zu vergleichen, wobei du dich darauf konzentrierst, wo der git-Autor vor dem Signieren des Tarballs geprüft wird. Fertig ist es, wenn ein falscher Autor erkannt wird, bevor der Release abgebrochen wird, und der Dry-Run-Modus dasselbe Problem erkennt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.