Document internal usage in confluence

• Type: Task
• Status: Closed
• Priority: Minor
• Resolution: Completed
• Affects Version/s: None
• Fix Version/s: 7.4.3.7 CE GA7, 7.4.13 DXP U3, Master
• Component/s: Feature Flags
• Labels: None
• Epic Link: Release Feature Flags

Document a guide to add a RFF to liferay-portal. Something similar to this article for Dev feature flags.

At the moment we just have this.