Add a new route for serving Remote Development WebIDE to GitLab

In the parent epic (Securely connect GitLab Web IDE to Remote VM/Co... (&8621 - closed)) we describe the following architecture of our second POC. To implement it, we need to serve WebIDE as a static website on GitLab.com behind a feature flag.

This issue is to create a new route on GitLab.com and serve the WebIDE on it.