Show user feedback widget on user onboarding

[spalmurray-codecov]

As part of the header/nav changes, we're removing the default floating Sentry user feedback widget and instead using a button in the new nav to open the modal. The one exception to this is in user onboarding, where we want to show the default floating Sentry user feedback widget.

This issue is to make the widget ONLY show on the user onboarding pages. This can be done with autoInject: false and manually triggering the widget on the relevant page.

This should be done AFTER the new header is fully rolled out and clean up is complete.