[5.x] Fix static caching invalidation for multi-sites

[duncanmcclean]

This pull request fixes some issues around Static Caching invalidation & Multi-sites, when the queue driver is set to anything other than sync.

When the DefaultInvalidator class passes down the invalidation rules from the config, it does so without specifying the domain in which the URLs should be invalidated.

cms/src/StaticCaching/DefaultInvalidator.php

Lines 70 to 72 in fd24694

	$this->cacher->invalidateUrls(
	Arr::get($this->rules, "collections.{$entry->collectionHandle()}.urls")
	);

The invalidateUrls method attempts to get the domain from the invalidation URLs in the config (which is why the mentioned workaround works).

When an invalidation rule doesn't include a domain, it'll attempt to get the site's "base URL" using AbstractCacher::getBaseUrl():

cms/src/StaticCaching/Cachers/AbstractCacher.php

Lines 49 to 62 in fd24694

	public function getBaseUrl()
	{
	// Check 'base_url' for backward compatibility.
	if (! $baseUrl = $this->config('base_url')) {
	// This could potentially just be Site::current()->absoluteUrl() but at the
	// moment that method gets the URL based on the request. For now, we will
	// manually get it from the config, as to not break any existing sites.
	$baseUrl = Str::startsWith($url = Site::current()->url(), '/')
	? Str::removeRight(config('app.url'), '/').$url
	: $url;
	}
	return rtrim($baseUrl, '/');
	}

This method then calls Site::current() which gets the domain by getting the current site, based on the request URL.

However, since we're in the context of a queue, there is no request, so Statamic falls back to the "default" site URL, which causes the path on the intended site to not get invalidated (intended being the site the entry is associated with).

This pull request attempts to fix this by including the domain in the array of URLs passed to invalidateUrls.

Fixes #7691.
Replaces #10517.

[duncanmcclean]

This is ready for review now.

The only thing I noticed while testing this PR on a real site was the fact that the GlobalVariablesSaved event is dispatched for every site whenever one site's globals are updated.

This means that whenever you update a global set, the global set will be invalidated in all sites, rather than just the site the global was just updated in.

I've opened a separate issue for that, as it'll likely require a breaking change in order to fix: #10888