Describe etcd's user roles

## Overview

In an "Overview" or "Start here" page, outline etcd's user roles or personas, including:
- *Evaluator*: Someone trying to determine whether etcd is appropriate for their product, project, or organization.
- *Admin or Operator*: Someone reponsible for setting up and maintaining a standalone (non-Kubernetes-backstore) production etcd service.
- *Kubernetes Admin*: Someone responsible for a Kubernetes cluster using etcd as a backstore.
- *Developer*: Someone incorporating or integrating etcd into an application or service.

In each user role section, provide a link to the beginning of a "getting started" workflow, either a Quick-start or Installation instructions.

Audience: All.

Type: Conceptual

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

Related material in the current doc:
- https://github.com/etcd-io/website/tree/main/content/en/docs/2.13/deploy/