fix(previews): preview doesn't work as expected when Faust configured

[ahuseyn]

When Faust enabled and "Front-end site URL" entered in the settings, it overrides the default behavior of HWP Previews.

NOTE: Removing "Front-end site URL" from Faust settings seems to fix this issue

This is what you get by clicking the preview button with the config below:

• Faust enabled, front-end URL set

Expected:

Should've opened default WordPress preview template with an iframe, showing frontend

Observed:

It redirects to the frontend URL defined in Faust settings, with different parameters than specified in HWP previews

This is for redirected previews in HWP Previews:

• Faust enabled, front-end URL set

Expected:

Should've redirected to the URL specified in HWP previews plugin

Observed:

Redirects to the domain specified in HWP Previews plugin, without respecting the parameters

[colinmurphy]

@ahuseyn @wpengine/headless-open-source @wpengine-cpierce

One option might be:

1. Add a config option to Faust to disable previews
2. Use the activation hook in HWP Previews to disable Faust Previews (whether that is in Faust or HWP Previews I am not sure).

[ahuseyn]

@colinmurphy @wpengine/headless-open-source
Redirected previews conflict will be fixed with #240. iframe conflict however is a bit complicated. Faust provides a filter to disable frontend redirects for the specific URLs, but those URLs have to be exact match. Thus all the preview URLs have to be supplied to that filter to disable redirects as far as I understand.

On the other hand, and more importantly we don't want to suppress the redirect feature of Faust (an independent plugin) for an optional feature (iframe) of HWP Previews. Instead I'll document this conflict in #229 and provide an instruction on how to resolve this conflict, by removing frontend_url from Faust.