title: Add Swagger base path field in Nest.js project
body: <p>I am trying to use nestjs/swagger to create a swagger file from my back-end and I am facing a problem related to the base path. What I want to achieve is to show version as base path instead of showing it in all the methods available, which is ugly and confusing.</p>
  
  <p>My API, right now, has the following structure (this is a set of what is present in <code>app.module.ts</code>):</p>
  
  <pre class="lang-js prettyprint-override"><code>const routes: Routes = [
    {
      path: '/api',
      module: ApiModule,
      children: [
        {
          path: '/v1',
          module: V1Module,
          children: [
            {
              path: '/orders',
              module: OrdersModule
            },
            {
              path: '/users',
              module: UsersModule
            }
          ]
        }
      ]
    }
  ];
  </code></pre>
  
  <p>This way, once I generate and check the swagger, I see all my methods following the <code>/api/v1</code> prefix. This could be an example:</p>
  
  <p><strong>orders</strong></p>
  
  <pre><code>GET   /api/v1/orders
  POST  /api/v1/orders
  GET   /api/v1/orders/{order_id}
  ...
  </code></pre>
  
  <p><strong>users</strong></p>
  
  <pre><code>GET   /api/v1/users
  POST  /api/v1/users
  GET   /api/v1/users/{user_id}
  ...
  </code></pre>
  
  <p>What I want is to get rid of <code>/api/v1</code> appearing in any method. I know that SWAGGER has fields for <code>host</code> and <code>basePath</code>, but do not find any way to populate it in Nest.js. Researching, I have found that there were <code>.setBasePath()</code> and <code>.addServer()</code> methods, but they do not work for me (I am pretty sure they are deprecated).</p>
  
  <p>Thank very much for your help.</p>