Consolidate all reference information

## Overview

Consolidate all reference information to a reference-specific section.

Or, create user role-specific reference sections within the Developer and Operations guides. Since some of the material overlaps, a single reference section is probably easier.

Reference documentation includes API, CLI, and configuration references, the glossary -- any topic that presents a comprehensive "lookup" document.

Audience: All

Type: Reference

The existing documentation might contain helpful source material that you can pull into this doc change. See recommendations for the existing (at the time of the CNCF tech doc analysis) etcd technical documentation pages:
https://github.com/cncf/techdocs/blob/main/assessments/0010-etcd/etcd-implementation.md/#general-reorganization

## 🎤 Context

This issue tracks recommended changes resulting from an analysis of the etcd documentation commissioned by CNCF. The analysis and supporting documents are here: https://github.com/cncf/techdocs/tree/main/assessments/0010-etcd/

## ✌️ Possible Implementation

The top-level Reference section should be clearly labeled as such and visible from everywhere in the documentation; the best place is probably as a top-level entry in the table of contents (TOC) that appears in the left sidebar. The TOC link should bring up an index of all reference pages with links.

If there is documentation that's auto-generated or extracted from code (APIs, for example), it's permissible -- preferred, in fact -- to link to such documentation. This avoids the churn and errors that accompany duplicating and trying to maintain such documentation in two locations.