Expose the "message" of a pod from argo get/watch to subsequent steps

# Summary

An Argo variable `{{steps.X.message}}` (or maybe `{{steps.X.outputs.message}}`) should include the message information that is displayed in `argo get` / `argo watch` so later steps can act accordingly.

# Motivation

I work with nodes with sometimes fail for a variety of reasons: `failed with exit code 1`, `pod deleted`, `the node had condition: [MemoryPressure]`, and more. I would like expose this message to later steps for proper processing; for instance, if the message is `pod deleted`, I would like to run it again, but I currently have to handle that sort of logic outside the workflow.

# Proposal

This information seems accessible, since it's included in `argo get`. It seems simple to annotate it like with the `exitCode`.

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**Message from the maintainers**:

If you wish to see this enhancement implemented please add a 👍 reaction to this issue! We often sort issues this way to know what to prioritize.

Trace how the message displayed by `argo get` and `argo watch` is produced, then compare it with the existing `exitCode` exposure. Done means a later workflow step can reference the pod message through the proposed variable and use it for conditional processing.

Written by the indexing model from the issue text.