Add cosa supermin-run

This is very close to `cosa supermin-shell` but instead expects a
command to run inside the supermin VM. Essentially, it's a very thin
wrapper around the `runvm` family of functions in `cmdlib.sh`.

By having it be a dedicated function, it becomes like a utility command
to have easy access to a privileged environment, with the working dir
automatically mounted in, podman remote proxying, etc... Note also this
*does not* require a cosa workdir.

The podman machine OS pipeline will be using this temporarily.

Author: jlebon

src/cmd-supermin-run

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -eou pipefail
+
+dn=$(dirname "$0")
+# shellcheck source=src/cmdlib.sh
+. "${dn}"/cmdlib.sh
+
+if [ ! -d tmp ]; then
+    echo 'Need tmp/ dir for supermin to work' >&2
+    exit 1
+fi
+
+workdir=$(pwd)
+export workdir
+
+case "${CACHE:-}" in
+  "") RUNVM=runvm;;
+  on) RUNVM=runvm_with_cache;;
+  snapshot) RUNVM=runvm_with_cache_snapshot;;
+  *) echo "CACHE=$CACHE is invalid" >&2; exit 1;;
+esac
+
+$RUNVM -- "$@"