UI: multi-select for input parameters

# Summary

Multi-select in the UI for input parameters

## Use Cases

Trigger workflow manually with multi-select input.

This is a reference to the old popular closed issue https://github.com/argoproj/argo-workflows/issues/6824

Thanks for considering this feature. Great OSS project!

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**Message from the maintainers**:

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The issue names no implementation files, tests, or entry points. Start by reviewing the existing UI for manually triggered workflow inputs and the referenced issue #6824. Done means defining and implementing multi-select input support for manually triggered workflows, with coverage for the resulting interaction.

Written by the indexing model from the issue text.