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/utils.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+# We need root access, but also appropriate envvar values. Require scripts to
+# run with sudo as a normal user
+ensure_env() {
+  RC=false
+  [ $EUID -eq 0 ] && [ -n "$SUDO_USER" ] && [ "$SUDO_USER" != "root" ] && RC=true
+  if $RC; then
+    export SETUP_USER="$SUDO_USER"
+    export SETUP_HOME="$HOME"
+  else
+    echo "Please run \"$0\" via sudo as a normal user"
+  fi
+  $RC
+}
+