[Improvement] Allow creating Run In Insomnia buttons to private export links

Our insomnia exports are stored in private repositories, and it would be nice to be able to add these buttons to our internal documentation

I attempted to use an `insomnia://` file handler that caused the browser to open Insomnia to export but it doesn't seem to work that way

If there is a related file handler, mentioning it and how to use it in the docs would be super useful.
Else some way to launch private links would be greatly appreciated.

Would just like to say thank you for Insomnia, great piece of software

No files, tests, or entry points are named. Start by locating the existing Run In Insomnia/private export-link handling and any documentation for the insomnia:// file handler; done means private export links can launch Insomnia or the supported handler is documented for internal use.

Written by the indexing model from the issue text.