[Doc request] Etcd and etcdctl

# Feature request

## Summary

Would be very nice to have the docs for etcd and etcdctl, as afaik they are commonly used within for example k8s

## Examples

v2.3: (not the current version, but still _very_ commonly used
v3.5:

The request names etcd and etcdctl and links to the etcd v2.3 and v3.5 documentation. No repository files, tests, or entry points are identified, so start by locating how existing API documentation sources are added. Done means the requested etcd and etcdctl documentation is available in DevDocs.

Written by the indexing model from the issue text.