NIFI-13455 Add Apache RAT License Checking

[exceptionfactory]

Summary

NIFI-13455 Adds license checking using Apache Rat. The check-licenses.sh shell script downloads the Apache Rat JAR to a cache directory and evaluates the output for unknown licenses. Apache Rat supports the SPDX-License-Identifier in files with the need for a complete license header.

The check-licenses.sh script can be run on a Linux or macOS and is incorporated in the GitHub build workflow.

Tracking

Please complete the following tracking steps prior to pull request creation.

Issue Tracking

• Apache NiFi Jira issue created

Pull Request Tracking

• Pull Request title starts with Apache NiFi Jira issue number, such as NIFI-00000
• Pull Request commit message starts with Apache NiFi Jira issue number, as such NIFI-00000

Pull Request Formatting

• Pull Request based on current revision of the main branch
• Pull Request refers to a feature branch with one commit containing changes