Prepare for 6.6.0 release

[MarkEWaite]

Prepare for 6.6.0 release

Set version number in pom

Testing done

Confirmed that tests pass on Linux. Rely on ci.jenkins.io for Windows.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed