Update Experiments API page based on initial review
Issue description
This page describes product documentation work that was identified during a documentation review of documentation pages associated with the Growth:Expansion stage/group.
Page: https://docs.gitlab.com/ee/api/experiments.html
Identified items
- Page isn't cross-linked from https://docs.gitlab.com/ee/development/experiment_guide/index.html but should be
- Page is missing from left nav gitlab-docs!1577 (merged)