Readarr /search endpoint, fix type mismatch in AddAuthorOptions struct

[Inku0]

Hey there, this is my first PR to an open source project, apologies in advance for any mistakes!

While attempting to create a Jellyseerr-like interface for Readarr, I didn't manage to find any way to search for books. Only the /book/lookup endpoint was implemented, but the results I got from it were lacking (no cover images, no book overview, no full author name). After adding the /search endpoint, I wasn't able to successfully call AddBook because Readarr expects the BooksToMonitor array to consist of strings instead of int64s.

So this PR adds the /search endpoint (https://readarr.com/docs/api/#/Search/get_api_v1_search) and fixes a type mismatch ([]int64 instead of []string) in the AddAuthorOptions struct. Readarr API docs:

I also added testing for the new search functionality in search_test.go, but I'm not 100% sure that it's up to par.

[bakerboy448]

For key context, Readarr is officially retired, and the official metadata server has been decommissioned. Therefore, I suggest making minimal MVP-type efforts towards Readarr API, as it will eventually be replaced by some future book automation app. Hopefully, this replacement will occur before Goodreads’ self-metadata data stops working.

just want to ensure efforts are prioritized appropriately for an effectively dead app

[Inku0]

Yep, unfortunately I'm well aware that Readarr got archived, although I'm currently trying out a newer fork (https://github.com/pennydreadful/bookshelf) alongside another metadata provider (https://github.com/blampe/rreading-glasses) and so far I've got it working without any major problems.

[davidnewhall]

Thanks!