Extender and improvements

• Added extender to allow other extensions to add data to existing indexes.
• Extensions can also make any Eloquent model compatible with Scout just by using the extender (and writing the appropriate full text gambit to fetch results from Scout).
• Allowed customization of the number of search results requested from the search engine, if not specified, it will be 200 for Meilisearch and null for other engines to fall back to their own defaults.
• Allowed usage of asynchronous queues to sync indexes, use new setting in admin to enable.
• Fixed post index not being removed on discussion delete (would not cause problems, but creates a lot of stale records after a while).
• All CLI commands can now be called with the native Eloquent model path instead of alternative model names, just like in Laravel.

You probably don't need to rebuild your indexes, their format has not changed. Check the README for the list of commands if needed.

This is a major update. You need to run composer require clarkwinkelmann/flarum-ext-scout to upgrade (update will not work unless you set the requirement to * which I do not recommend for this experimental extension)

Developers can read the documentation in the README file to integrate their own extensions with the index. Currently only my closed-source Formulaire extension uses the extender. Over the next few weeks, most of the Flamarkt extensions will get Scout support and can serve as implementation examples.