Kubeflow v1.8.1

This is the official release of Kubeflow 1.8.1. It supports Kubernetes 1.27 which provides a clear migration path to Kubeflow 1.9.

The specific versions of each component can be found in the README.

1.8.1 include the following updates from Serving and Pipelines WGs:

Serving WG
Pipelines WG

Fixes:
pipelines/backend: Parameterizing v2 Launcher and Driver Images
pipelines/backend: Pipeline and PipelineVersion Description column value should be optional.
pipelines/frontend: Support running old v1 pipeline.