FT: Plugin Context Data Sharing

[rhuss]

In order to allow kn to reuse some (stateful) context that is provided by a plugin, I'm proposing to extend the "plugin contract". The original use case is to share the namespace and name of a function managed by kn-plugin-func that is stored in a local "func.yaml" file. kn must not directly read this file as this would introduce a dependency from kn to kn-func-plugin (in the wrong direction).

The Feature Track Kn Plugin Context Data Sharing will describe the design, this issue is to track the work on this FT.

The current status is "WIP" and "pre Draft" but want to share early.