Improve copying asset URLs in devstack deployments

[samuelallan72]

This issue was also raised at https://discuss.openedx.org/t/unable-to-copy-studio-or-web-url-in-frontend-app-authoring-teak-sumac-release/16980

Background: the web Clipboard API is only available in a secure context - ie. over https or served from localhost. For anything non-localhost domain served over http, the clipboard API is not available.

The trouble is that a standard Tutor devstack is served over http, from the local.openedx.io domain. This is fine for development, but the Clipboard API is not available.

Currently, frontend-app-authoring crashes in this case, where the Clipboard API is not available. It would be nice if it had a graceful fallback (eg. a notification that clipboard api is not available, or simply not displaying the "copy to clipboard" buttons).

Also it would be good if the full urls were shown somewhere; currently they are cut off with ellipsis, which currently makes it impossible to manually copy the url if the clipboard api is not available.

[bradenmacdonald]

It may also be possible to get it working in development environments by using execCommand from a click handler rather than using the Clipboard API.

[bradenmacdonald]

This PR: #2937 in src/course-outline/outline-sidebar/info-sidebar/UnitInfoSidebar.tsx is using execCommand as a fallback, and it's working great. We need to apply the same fix to the Files & Uploads page by factoring it out as a reusable helper function.