Support authentication for import URLs in JSM Assets

Issue Summary

When importing CSV or JSON files via URL in JSM Assets, the URL currently needs to be publicly accessible. This prevents the use of the feature for private/confidential information due to privacy vulnerabilities. 

Suggested Solution

Support authentication to allow for private URLs.

Workaround

1) Manually import the CSON or CSV file by uploading it to Assets.

OR

2) Adjust the URL to be publicly accessible.

Mitigation

Limit exposure of URLs to the 'Atlassian domains' as outlined here, and in more granular shape here.