Knative Client release v0.16.1

This minor update contains backports of essential fix and some minor feature additions.
See the CHANGELOG for full details.

Fixes:

• Fix missing NAMESPACE column header for 'kn source list -A
• Fix exit code for kn service delete and kn revision delete failures
• Fix client side volume name generation
• kn source list output now has client custom GVK set as {Group: client.knative.dev, Version: v1alpha1, Kind: SourceList}
• fix(kn source list): list inbuilt sources if crd access is restricted
• fix(tekton e2e): Refer tasks from new tekton catalog task structure
• Add support for internal plugins