Allow multiple transitions with the same name

This works in Symfony's Workflow but laravel-workflow doesn't have a way to reference multiple transitions with the same name in the config file. This patch adds support for the alternative notation referenced in symfony/symfony#22558 that uses a `name` field rather than inferring the transition name from the key.

E.g.

```
	't1' => [
		'from' => 'a',
		'to' => 'b',
	]
```

becomes

```
	[
		'name' => 't1',
		'from' => 'a',
		'to' => 'b',
	]
```

which allows multiple transitions with the same name.

Author: laurenkt

src/WorkflowRegistry.php

@@ -48,6 +48,10 @@ public function __construct(array $config)
             $builder = new DefinitionBuilder($workflowData['places']);
 
             foreach ($workflowData['transitions'] as $transitionName => $transition) {
+                if (!is_string($transitionName)) {
+                    $transitionName = $transition['name'];
+                }
+
                 $builder->addTransition(new Transition($transitionName, $transition['from'], $transition['to']));
             }