Add metadata to Charts and Omnibus docs

Issue Description

The product documentation pages in the charts and omnibus-gitlab repos need the following metadata to be added to them:

---
stage: Enablement
group: Distribution
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
---

Passing this along to @aqualls and mentioning @axil for awareness. Thanks, @aqualls .