Create a "Getting started with `etcdctl`" page

[nate-double-u]

trafficstars

As per #65:

Getting Started with Etcdctl - page with simple instructions on how to install and get started with Etcdctl, including authentication to existing clusters.

This page could be linked to from both the Quickstart and Install pages, but should stand on its own content wise.

[nate-double-u]

https://etcd.io/docs/v3.5/dev-guide/interacting_v3/ may be a good base/starting point for this page.

[spzala]

https://github.com/etcd-io/etcd/tree/main/etcdutl

[nate-double-u]

/cc @Somoshree

[Somoshree]

/assign