config-management-plugins.md does not describe the input and output of a plugin

[MikeSpreitzer]

Checklist:

• I've searched in the docs and FAQ for my answer: https://bit.ly/argocd-faq.
• I've included steps to reproduce the bug.
• I've pasted the output of argocd version.

Describe the bug

I wanted to understand plugins, so I went looking through the documentation. Somewhere I found a statement that the output of a plugin should be JSON or YAML, but no details on what that JSON or YAML is. I think the missing statement is something along the lines of saying that the output should be JSON or YAML that defines the kube API objects that the plugin is saying should go to the kube cluster.

I did eventually find a page focused on plugins, https://github.com/argoproj/argo-cd/blob/master/docs/user-guide/config-management-plugins.md . The statement about output belongs on that page. BTW, that page should be easier to find (linked from other places that reference it). Also, I did not find anywhere a statement about what the input to a plugin is. I think that also belongs on this page. If I understand correctly, the input is the contents of the current working directory, which is set to the path of the Application, relative to a git checkout of the commit referenced by the Application.

To Reproduce

Read the docs.

Expected behavior

Easily finding a clear statement of what are the inputs and outputs of a plugin.

Screenshots

N/A

Version

The master branch.

Logs

N/A