Allow admin role to create pre-signed URLs with arbitrary expirations

[spakanati]

User roles are bound by the default bucket expiration in the storage.buckets table, but admin should be able to generate presigned URLs with longer expirations if needed.

Per Discord discussion, there are some use cases when a longer expiration is useful (i.e. in serverless functions when needing to send the URL to external services but immediate download can't be guaranteed) and admin should be able to override the default expiration settings when necessary.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.