cli: Add setup and firstboot commands

This adds two new top-level commands: setup and firstboot.

Firstboot is pure-golang implementation of a service that runs some
commands once when a system first boots. You need to install this
service, and put the scripts to run in a special directory. This is
inspired by the virt-builder --firstboot mechanism.

Setup is a general purpose command that makes it easy to setup certain
facilities on a new machine. These include the mgmt package dependencies
it might need, a service to run it from, and the necessary service to
use the mgmt firstboot service as well.

All of this has been built to facilitate handoff between provisioning a
new machine and running configuration management on it.

firstboot/firstboot.go

@@ -0,0 +1,53 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+// Package firstboot provides a service that runs scripts once on first boot.
+// You can easily test this with:
+//
+// mkdir /tmp/mgmt-firstboot/ ; echo 'echo hello' > /tmp/mgmt-firstboot/foo.sh
+// ./mgmt firstboot start --lock-file-path=/tmp/flock.lock \
+// --scripts-dir=/tmp/mgmt-firstboot/ --logging-dir=/tmp/
+package firstboot
+
+import (
+	"context"
+)
+
+// API is the simple interface we expect for any setup items.
+type API interface {
+	// Main runs everything for this setup item.
+	Main(context.Context) error
+}
+
+// Config is a struct of all the configuration values which are shared by all of
+// the setup utilities. By including this as a separate struct, it can be used
+// as part of the API if we want.
+type Config struct {
+	//Foo string `arg:"--foo,env:MGMT_FIRSTBOOT_FOO" help:"Foo..."` // TODO: foo
+}