[cloud] fix org invites not working if user is not logged in

Created by: kopancek

Description

The fix is actually making sure the whole organizations section can only be accessed by authenticated users. It does not really make sense to allow non-authenticated users to view it.

Related Jira issue

https://sourcegraph.atlassian.net/browse/CLOUD-152

Testing locally

1. Run sg in cloud mode: sg start dotcom
2. Create an organization
3. Invite another user to the organization
4. In an incognito window, open the invite link immediately, without logging in
5. You should be redirected to the login screen
6. After logging in or signing up, you should be redirected back to the org invite screen