Code Insights: Hide Code Insights global nav-bar item for the cloud accounts

Created by: vovakulikov

This PR adds a temporal gate check since the cloud landing page hasn't been released yet and the cloud itself doesn't support code insights yet. Remove this check when the code insights cloud landing page will be released. In this PR https://github.com/sourcegraph/sourcegraph/pull/31704

Test plan

• Check that cloud account (sign in/sign out) can't see the code insights navbar item