NIFI-12396 Add python3-venv to Dockerfile for dockerhub

[exceptionfactory]

Summary

NIFI-12396 Adds the python3-env package to the Dockerfile in the dockerhub module for NiFi, following the same settings in the dockermaven configuration. This package is necessary to run Python extensions in the Docker Hub container.

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

Verification

Please indicate the verification steps performed prior to pull request creation.

Build

• Build completed using mvn 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

[lordgamez]

LGTM, thanks for the quick fix!