Make Argo UI not indexed

[crenshaw-dev]

Checklist:

• I've included the version.
• I've included reproduction steps.
• I've included the workflow YAML.
• I've included the logs.

What happened:

I noticed Argo UI doesn't prevent search engine indexing.

What you expected to happen:

I expected Argo UI to prevent search engine indexing. If someone leaves an Argo UI public-facing accidentally, we probably want it to be not super discoverable.

How to reproduce it (as minimally and precisely as possible):

Inspect the source code of the Argo UI. Search for noindex, and you won't find any results.

Anything else we need to know?:

Environment:

• Argo version: 2.6.0

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Message from the maintainers:

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[simster7]

Care to submit a PR? :)

[simster7]

Closed with #2383