Move code suggestions to Premium

Overview

GitLab offers Code Suggestions feature to write code more efficiently by viewing code suggestions as you type in Ultimate.

Proposal

• Move Code Suggestions from Ultimate to Premium. Update associated specs and documentation.

Issue readiness

• Product: issue description is accurate with an acceptable proposal for an MVC
• Engineering: issue is implementable with few remaining questions, is sufficiently broken down, and is able to be estimated

Availability & Testing

Since this is a minor change, we would probably not need any automated test changes. However, we should manually test this to ensure that a Premium user is able to access the feature and that the Gold customer did not lose it.