Add Max Concurrent Connections for database users

Closes #1849

Allows database users to be limited to a number of concurrent connections to prevent one user from connecting hundreds of time and bottlenecking the MySQL server.

app/Transformers/Api/Application/ServerDatabaseTransformer.php

@@ -56,6 +56,7 @@ class ServerDatabaseTransformer extends BaseTransformer
             'database' => $model->database,
             'username' => $model->username,
             'remote' => $model->remote,
+            'max_connections' => $model->max_connections,
             'created_at' => Chronos::createFromFormat(Chronos::DEFAULT_TO_STRING_FORMAT, $model->created_at)
                 ->setTimezone(config('app.timezone'))
                 ->toIso8601String(),