Multi-cluster, multi-namespace workflows

# Summary

Run workflows across multiple clusters.

# Motivation

So you only need to run one Argo Workflows installation.
So you can run a workflow that has nodes in different clusters.

# Proposal

Like Argo CD.

#3516

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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.

Review the proposal in #3516 and the linked closed pull request #4781 before starting, since this issue does not identify implementation files or tests. Define the supported multi-cluster and multi-namespace workflow behavior, including nodes in different clusters, and establish tests that demonstrate those scenarios work.

Written by the indexing model from the issue text.