Abstract the key to easier override (#156)

* Abstract the key to easier override

Spoke with Joe about this idea via email.

We need the ability to change the key in our app. Specifically because we a prefix in `config/filesystems.php` and use the same bucket across multiple staging environments.

Per the discussion we would need to override the controller and customize it ourselves.

It would be helpful if the key was abstracted so we didn't have to duplicate the entire logic in `store`

* Update SignedStorageUrlController.php

---------

Co-authored-by: Taylor Otwell <[email protected]>

src/Http/Controllers/SignedStorageUrlController.php

@@ -34,7 +34,7 @@ public function store(Request $request)
         $expiresAfter = config('vapor.signed_storage_url_expires_after', 5);
 
         $signedRequest = $client->createPresignedRequest(
-            $this->createCommand($request, $client, $bucket, $key = ('tmp/'.$uuid)),
+            $this->createCommand($request, $client, $bucket, $key = $this->getKey($uuid)),
             sprintf('+%s minutes', $expiresAfter)
         );
 
@@ -141,6 +141,17 @@ protected function storageClient()
         return new S3Client($config);
     }
 
+    /**
+     * Get key for the given UUID.
+     *
+     * @param  string  $uuid
+     * @return string
+     */
+    protected function getKey(string $uuid)
+    {
+        return 'tmp/'.$uuid;
+    }
+
     /**
      * Get the default visibility for uploads.
      *