Bump pipeline-model-definition to v1.9.1

[bitwiseman]

Depends on #587

• 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 demonstrates feature works or fixes the issue

[basil]

Thanks for the PR! This certainly works as a downstream of #587. Though I fear that it is going to take a long time to merge any of the PRs that are open right now (including #587) due to the fact that the main branch is currently unstable and GitHub is set up not to allow any merges that don't have a passing CI run. I'll try and help as I have the time, but any assistance would be appreciated.