Frontend proxied requests fallback to PWA if not in allow list causing error

[justinconabree]

In Venia it's possible to define a particular path (or pattern) to resolve through a proxy. If the URL is a front-end URL and is not set in the front_names_to_skip configuration, it tries to reserve the PWA, looping, which causes an error.

All proxied requests should return the original front-name in the AreaList plugin.

This can be achieved by setting a header in the UPWARD PHP Proxy resolver and checking for the header in the AreaList plugin