task: Update kubectl kcp plugin checks in local-setup and docs

[ntnn]

Overview

1. local-setup example-data requires the kubectl create-workspace plugin but the environment check does not verify it is present
2. Docs only references the kubeclt-kcp plugin, but not others: https://platform-mesh.io/release-0.3/how-to-guides/set-up-platform-mesh-locally.html
3. Docs has no link on how to setup the plugins

Implementation Details

Adjust the local-setup scripts to verify all plugins are installed.
Potentially add a task to install the plugins.
Adjust the docs to document at least a link to install the plugins.

Completion Checklist

• Code implemented and tested
• Documentation updated
• Changes reviewed