Added configurable API throttling, Handled API errors standardly

app/Http/Kernel.php

@@ -32,7 +32,7 @@ class Kernel extends HttpKernel
             \BookStack\Http\Middleware\GlobalViewData::class,
         ],
         'api' => [
-            'throttle:60,1',
+            \BookStack\Http\Middleware\ThrottleApiRequests::class,
             \BookStack\Http\Middleware\EncryptCookies::class,
             \BookStack\Http\Middleware\StartSessionIfCookieExists::class,
             \BookStack\Http\Middleware\ApiAuthenticate::class,

app/Http/Middleware/ThrottleApiRequests.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace BookStack\Http\Middleware;
+
+use Illuminate\Routing\Middleware\ThrottleRequests as Middleware;
+
+class ThrottleApiRequests extends Middleware
+{
+
+    /**
+     * Resolve the number of attempts if the user is authenticated or not.
+     */
+    protected function resolveMaxAttempts($request, $maxAttempts)
+    {
+        return (int) config('api.requests_per_minute');
+    }
+
+}