Unify kn workflow plugin names and its usages in SonataFlow Guides

[LuboTerifaj]

Unify kn workflow plugin names and their usages in SonataFlow Guides.

Details

There are various names used within the Guides:

• Knative Workflow CLI
• SonataFlow plug-in for Knative CLI
• kn-plugin-workflow

Users may get confused very easily.

Acceptance criteria

It can be easily identified from the documentation what is the official name of the extension.

[LuboTerifaj]

Hello @kaldesai, I cannot assign the task to you. Feel free to redistribute the issue as needed. cc @domhanak @tomasdavidorg Thanks!