[bamaer]

• add the PIPELINE_GRAPH event kind with PipelineGraphLineagePayload (enabled hops, in pipeline order)
• emit it once per pipeline run, next to STARTED, with the same context
• document that sinks skip event kinds they do not handle
• the OpenLineage sink ignores the new kind, so its output does not change yet

Please add a meaningful description for your change here

---

Thank you for your contribution! Follow this checklist to help us incorporate your contribution quickly and easily:

• Run mvn clean install apache-rat:check to make sure basic checks pass. A more thorough check will be performed on your pull request automatically.
• If you have a group of commits related to the same change, please squash your commits into one and force push your branch using git rebase -i.
• Mention the appropriate issue in your description (for example: addresses #123), if applicable.

To make clear that you license your contribution under the Apache License Version 2.0, January 2004
you have to acknowledge this by using the following check-box.

• I hereby declare this contribution to be licensed under the Apache License Version 2.0, January 2004
• In any other case, please file an Apache Individual Contributor License Agreement.