Add warning about permissions to install to the download prompt for Companion App

Summary

The download prompt that is displayed the first time selects 'Edit with' in file preview, should have a warning to users that they need permissions to download and install on the local machine.

Current behaviour

The Download and install the Atlassian Companion app mentions the option to distribute the app, in case users aren't able to install applications themselves. But the prompt that is displayed does not give the same warning, so most users will attempt to download and install the app

Desired behaviour

The download prompt could containing a warning message, like:
Warning, you'll need to have permissions to download and install the application locally. If that is not the case, or you are not sure, please contact your administrator.