NIFI-13824 Install processor dependencies in one go

[fgerlits]

Summary

NIFI-13824

If a Python processor defines dependencies both inline and in a requirements.txt file, then we need to install the two groups of dependencies in a single pip install command, otherwise pip is not able to resolve the web of dependencies correctly.

Tracking

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Issue Tracking

• [x] Apache NiFi Jira issue created

Pull Request Tracking

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

Pull Request Formatting

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• [x] Pull Request refers to a feature branch with one commit containing changes

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Build

• [ ] Build completed using ./mvnw clean install -P contrib-check
  • [ ] JDK 21

Licensing

• [ ] New dependencies are compatible with the Apache License 2.0 according to the License Policy
• [ ] New dependencies are documented in applicable LICENSE and NOTICE files

Documentation

• [ ] Documentation formatting appears as expected in rendered files

[fgerlits]

the new Python unit test is failing on both macOS and Ubuntu Linux

This was because we need to set PYTHON_CMD for some of the Python code to work; fixed in 3889d12beb6162172ca5ee70c7ec9a47a9450210