Pass request headers along to initial browser page used to gather stories

[wwilsman]

The problem

If a Storybook build is served behind an authenticated server, authorization credentials should be able to be provided to the initial page that collects Storybook stories (and also the Storybook version).

The discovery authorization options only work during request interception, so we cannot provide those with these initial pages as we don't want to capture any resources yet. We can however still provide request-headers.