As Jobin said, it is an admin permitted functionality. Also it is not a good thing giving permission to user who can import unneccessary data into database.
FYI, External System Import( which has Import CSV functionality) is present in a bundled plugin called jira-importers-plugin. If you still want to give permission customize this plugin and build it.
Also I don't know whether you can install or not as you are asking for OnDemand.
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