📝 Description

When running MLRun in multi-user mode (with Kubeflow Pipelines + Dex/OIDC authentication), calling create_pipeline results in a 403 Forbidden error from KFP. This happens because the namespace parameter is never passed through to KFP's create_experiment() call, so KFP defaults to the kubeflow namespace where the user has no permissions.

Fixes #9960.

🛠️ Changes Made

• server/py/services/api/api/endpoints/pipelines.py: added an optional namespace query parameter to the create_pipeline endpoint and forwarded it to the internal _create_pipeline() helper.
• server/py/services/api/crud/pipelines.py: Pipelines.create_pipeline() now accepts namespace and uses it both to initialize the KFP client (_initialize_kfp_client(namespace)) and when calling kfp_client.create_experiment(name=experiment_name, namespace=namespace), so the experiment is created in the caller's profile namespace instead of the default one.

✅ Checklist

• I updated the documentation (if applicable)
• I have tested the changes in this PR
• I confirmed whether my changes are covered by system tests
  • If yes, I ran all relevant system tests and ensured they passed before submitting this PR
  • I updated existing system tests and/or added new ones if needed to cover my changes
• If I introduced a deprecation:
  • I followed the Deprecation Guidelines
  • I updated the relevant Jira ticket for documentation
• Please run Smoke-tests workflow, providing it the PR number as input (upon success, the workflow run will add label "Smoke tests: Pass" to the PR)

🧪 Testing

• Verified namespace is correctly threaded end-to-end: endpoint → _create_pipeline → Pipelines.create_pipeline → _initialize_kfp_client(namespace) and kfp_client.create_experiment(namespace=namespace).
• ruff check and ruff format --check pass on both changed files.
• Validated in production on GKE and EKS clusters running MLRun 1.10.0 in multi-user mode with KFP 2.x and Dex authentication: before the fix, project.run(workflow_path=...) from a Jupyter notebook in a user profile namespace returned 403 Forbidden from KFP; after the fix, the pipeline is created successfully in the user's profile namespace.

🔗 References

• Ticket link: BUG: create_pipeline does not forward namespace to KFP create_experiment in multi-user mode — causes 403 Forbidden #9960
• Design docs links: N/A
• External links: N/A

🚨 Breaking Changes?

• Yes (explain below)
• No

The namespace parameter is optional and defaults to None, preserving existing behavior for single-user deployments.