Add sites hook to Sitemap class

[duncanmcclean]

This pull request adds a sites hook to the Sitemap class, allowing developers to override which sites should be used when generating a sitemap.

Useful for headless setups where you may only have a single domain, but you have multiple sites. You may want to determine the returned sites using a query parameter instead.

// app/Providers/AppServiceProvider.php

use Statamic\Facades\Site;
use Statamic\SeoPro\Sitemap\Sitemap;

Sitemap::hook('sites', function ($sites) {
    return Site::all()->filter(fn ($site) => $site->handle() === request()->site)->values();
});

Closes #437

[jerome2710]

@duncanmcclean that's quick, thank you! This looks like a solution we could use.

One observation, as the sitemap is cached with Cache::remember(Sitemap::CACHE_KEY.'_'.$key.'_index'), won't the output for all site be cached, regardless of the hook, as it's called later?

We would call /sitemap.xml?site=X and /sitemap.xml?site=Y, where I would assume site Y would also get the sitemap of site X, as this response is cached?

[duncanmcclean]

Good catch! I've opened #439 to address this which I'll merge and tag soon.