Priortise metadata calls by ISBN, not title. (or otherwise)

[sabrina553]

re: #1800 (comment)

as per my hardcover PR, there is merit to having a "base search" i,e, this provider will be called first, before any other provider.

for example, the hardcover and goodreads metadata work well in conjunction leveraging hardcover's precision in finding "popular/specific" editions and goodreads' accuracy in regards to metadata quality.

With ISBN as this default value the idea is that hardcover, finds said ISBN with it's more versatile API, and goodreads then only parses data by ISBN in the typical p1->4 method, and isn't used for more complicated calls, like finding non-audiobooks, language specific, or otherwise.

alternatively a "non-binding" variable could be used such as "search priority" though in my opinion this would cause confusion. Moreover ISBN as a sensible "ground" as it is the universal ID.