Move features to core: "Canary Deployments"

Overview

As part of an effort to open source some currently paid features and move them to our free tier "Canary Deployments" have been identified as a feature worth moving down.

Proposal

Canary deployments should be moved to Core. This requires the removal of any licensing checks for the feature which is currently in the Premium tier.

Parts :

1. CANARY_ENABLED in Auto DevOps. Already in core, just like incremental rollouts
2. "canary deploy boards" aka the "yellow dot" in deploy boards.
3. Advanced traffic control with Canary Ingress

Documentation

Documentation for this feature should be updated to reflect that this is no longer in a paid tier.

• Documentation: https://docs.gitlab.com/ee/user/project/canary_deployments.html
• Issue that implemented: #1659 (closed)