feat(ui): Support app booting with client-config API (#13940)
feat(ui): Support app booting with client-config API (#13940)

Allows the app to boot WITHOUT being provided __initialData. The app
will make an API request to the backend to hydrate itself.

This will currently only be used in experimental SPA mode, as there are
no places where the app is loaded without __initialData.
mvaled/sentry,beeftornado/sentry,beeftornado/sentry,mvaled/sentry,beeftornado/sentry,mvaled/sentry,mvaled/sentry,mvaled/sentry,mvaled/sentry