Migrate to Kitsu's GraphQL API (#3792)

While there are still some nasty corners (multiple shapes of error
response, unhandled error types on their end, etc.), this is a
functional, feature-parity replacement for the JSON:API API we were
using before.

According to the GraphQL docs, searching by title still goes via
Algolia.

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is a modified version of [Keep a Changelog](https://keepachangelog.co
 ## [Unreleased]
 ### Added
 - Add `id:` prefix search to remaining trackers (AniList, Bangumi, Kitsu, MangaUpdates, Shikimori, and Hikka) ([@MajorTanya](https://github.com/MajorTanya)) ([#3776](https://github.com/mihonapp/mihon/pull/3776))
+  - Allow `id:` to search for slugs on Kitsu ([@MajorTanya](https://github.com/MajorTanya)) ([#3792](https://github.com/mihonapp/mihon/pull/3792))
 - Add support for using the user's chosen rating system for Kitsu ([@MajorTanya](https://github.com/MajorTanya)) ([#3818](https://github.com/mihonapp/mihon/pull/3818))
 
 ### Improved