download artifacts with temp_queue if possible

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We currently download artifacts with queue, which uses the worker creds. This means for private artifacts, the worker clientId needs to have access to those private artifacts.

The temp_queue will be given access to private artifacts for those tasks that need them. So if we download artifacts with that, we no longer need to add private artifact support to the worker clientId. Let's do that.

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We need to re-land, once we add the appropriate get-artifact scopes for all partners. https://bugzilla.mozilla.org/show_bug.cgi?id=1618138

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https://bugzilla.mozilla.org/show_bug.cgi?id=1594797#c3
#437