Fixup scripts to set up a new CI node (#9348)

* Clean up node setup scripts for new CI boxes

* Move files under ci directory

* Set CUDA env var to setup cuda drivers

* Fixup and add README

* shellcheck

* Apply review feedback, rename dir and setup files

Co-authored-by: publish-docs.sh <maintainers@solana.com>

ci/setup-new-buildkite-agent/enable-buildkite.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+sudo systemctl daemon-reload
+sudo systemctl enable --now buildkite-agent