[2.2.4] [WIP] Respect custom connections when creating database (#244)

* Add TenantDatabaseManager::setConnection()

* Apply fixes from StyleCI

src/Contracts/Future/CanSetConnection.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Stancl\Tenancy\Contracts\Future;
+
+use Illuminate\Database\Connection;
+
+/**
+ * This interface *might* be part of the TenantDatabaseManager interface in 3.x.
+ */
+interface CanSetConnection
+{
+    public function setConnection(Connection $connection);
+}