Ensure we always set root pageTitle

[LeoMcA]

We have to do some weird handling in fred:

https://github.com/search?q=repo%3Amdn%2Ffred+%22pageTitle+%3D%22&type=code

See also: mdn/fred#693

[caugner]

We have to do some weird handling in fred:

What is weird about using doc.pageTitle as pageTitle?

Afaik doc is the content of the index.json, and all pages have a pageTitle, including the "Advertise with us" page, see: https://developer.mozilla.org/en-US/advertising/index.json

But good catch, we shouldn't need the special handling for the "Advertise with us" page anymore:

https://github.com/mdn/fred/blob/f4938f2cbf21725b4d7d80cc3f119b5fc6430874/components/advertising/server.js#L42-L43

[LeoMcA]

No, context is the content of the index.json, doc is a key within it: https://developer.mozilla.org/en-US/docs/Web/index.json