Try using apps/local end point to upload your app using a URI. So, if I were you, considering the example you gave I would do something like this
curl -1 -s -k -u admin:changeme https://localhost:8089/services/apps/local -d name=http://local.repo/files/splunk_apps/sideview-utils-lgpl_135.tgz -d filename=true
the extra filename parameter is for stating that the URI is a file indeed.
I hope this helps.
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