fix(docs): add RBAC and user to executor plugins example

[dgolja]

Fixes #13015

Motivation

Having a working example from the documentation.

Modifications

The main practical modification involves updating the user ID. Other changes, especially the RBAC role is to provide some guidance what permissions you need for the example to work (see).

Verification

Example provided in the documentation now works as expected.

[agilgur5]

A small copy-edit below and also a suggestion to unify Agent permissions docs

[agilgur5]

I think this block should go in the ## Configuration section above a subsection ### Permissions. It's more important than a "Note" -- this is required

[agilgur5]

The Argo "agent" is mentioned in the HTTP template docs as well. Ideally we'd unify them and have a page on the Agent that both link to with regard to permissions / more information. The Agent is poorly documented; I didn't even know much about it until a few months ago

Potentially a section in the existing Workflow RBAC page might make sense, which is what the quick-start manifest already links to

[agilgur5]

I would also leave the "If <= v3.2" out of this and leave it in the Workflow description annotation like the quick start manifest. Let's keep the two identical.

Even better would be to make that an in-line comment on the workflowtasksets/status line in both

[dgolja]

Let me know what you think about the latest change. I added the ### Permissions section with some relevant links and removed the Role definition. Not every user may experience permission issues, because it depends on how they installed WF. I think this new section letting them know they may need to adjust the permissions are adequate for now.

I agree that the documentation for the agent and permissions, in general, could be better. Let me think about it a bit more, and for now, I'll provide this as a stopgap. I may create a follow-up PR to improve the permissions documentation, but first, I need to dig more into the code to fully understand it.

[agilgur5]

I think this new section letting them know they may need to adjust the permissions are adequate for now.

Yea we'd still leave this section or something similar if we move the actual Agent docs to its own page; this section would just link to that, something like "Plugins use the Argo Agent, ensure you have appropriate RBAC for your Workflow".

Let me know what you think about the latest change.

It looks like the current text is mostly just a copy of the HTTP Template doc? That section causes confusion as-is the way it is written so if we're going to add it, I'd prefer to unify in the Workflow RBAC page. We can just have a short description there and show the RBAC. Can improve that in later PRs

I can help guide that if you're ok relying on my knowledge.