[4.x] Don't use onDeleteCascade in the migrations (#883)

* removed `cascade` on delete for domains

* removed only `onDelete` cascade

* keep impersonation migrations unchanged

* domains set null on delete

* Update 2019_09_15_000020_create_domains_table.php

* Added DeleteDomain Job while deleting tenant.

* Update assets/TenancyServiceProvider.stub.php

Co-authored-by: Samuel Štancl <samuel@archte.ch>

* renamed class

* Update DeleteDomains.php

* onDelete restrict

* revert nullable

* removed `shouldQueue` interface

* Update TenancyServiceProvider.stub.php

* fetch and delete domains individually

* Update DeleteDomains.php

* tests for `DeleteDomains` job

Co-authored-by: Samuel Štancl <samuel@archte.ch>

src/Jobs/DeleteDomains.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Stancl\Tenancy\Jobs;
+
+use Illuminate\Bus\Queueable;
+use Illuminate\Contracts\Queue\ShouldQueue;
+use Illuminate\Foundation\Bus\Dispatchable;
+use Illuminate\Queue\InteractsWithQueue;
+use Illuminate\Queue\SerializesModels;
+use Stancl\Tenancy\Contracts\TenantWithDatabase;
+use Stancl\Tenancy\Database\Models\Domain;
+use Stancl\Tenancy\Events\DatabaseDeleted;
+use Stancl\Tenancy\Events\DeletingDatabase;
+use Stancl\Tenancy\Events\DeletingDomain;
+use Stancl\Tenancy\Events\DomainDeleted;
+
+class DeleteDomains
+{
+    use Dispatchable, InteractsWithQueue, Queueable, SerializesModels;
+
+    /** @var TenantWithDatabase */
+    protected $tenant;
+
+    public function __construct(TenantWithDatabase $tenant)
+    {
+        $this->tenant = $tenant;
+    }
+
+    public function handle()
+    {
+        $this->tenant->domains->each->delete();
+    }
+}