Add Namespace Check to Resource List Command

[danielhelfand]

Following similar approaches outlined for tkn commands, this pull request is part of addressing #311. An error message has been added for tkn resource list when a namespace doesn't exist on a cluster.

Submitter Checklist

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• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
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Release Notes

Adds error message to tkn resource list command when a namespace does not exist

[tekton-robot]

Hi @danielhelfand. Thanks for your PR.

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[chmouel]

/ok-to-test

[piyush-garg]

/lgtm

[danielhelfand]

Note: Conflict with #384 here

[sthaha]

/approve

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: piyush-garg, sthaha

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