Revert "Get rid of TenantDatabaseDoesNotExist exception"

This reverts commit fe52a3c4ea.

src/Exceptions/TenantDatabaseDoesNotExistException.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Stancl\Tenancy\Exceptions;
+
+use Exception;
+
+class TenantDatabaseDoesNotExistException extends Exception
+{
+    public function __construct($database)
+    {
+        parent::__construct("Database $database does not exist.");
+    }
+}