Kubeflow 1.9.1 Release Candidate 1

The release includes the following platform/manifests/security changes:

• Kubernetes 1.31 support
• The Documentation has been overhauled
• The automatic CVE scanning with Trivy on the master branch workflow now lets you download the scanning results
• Rootless efforts in contrib/security continue

We also updated the following components:

• Kubeflow Pipelines 2.3.0, which includes Argo Workflows 3.4
• Training Operator v1.8.1
• KServe 0.13.1

TODO for RC 2:

• #2864
• #2880