Add logging - as similar behaviour as possible to `cvm-reverse-proxy`

[ameba23]

cvm-reverse-proxy has logging options:

	&cli.BoolFlag{
		Name:  "log-json",
		Value: false,
		Usage: "log in JSON format",
	},
	&cli.BoolFlag{
		Name:  "log-debug",
		Value: true,
		Usage: "log debug messages",
	},
	&cli.BoolFlag{
		Name:    "log-dcap-quote",
		EnvVars: []string{"LOG_DCAP_QUOTE"},
		Value:   false,
		Usage:   "log dcap quotes to folder quotes/",
	},

These should be re-created here using similar formatting.

type LoggingOpts struct {
	Debug   bool
	JSON    bool
	Service string
	Version string
}

func SetupLogger(opts *LoggingOpts) (log *slog.Logger) {
	logLevel := slog.LevelInfo
	if opts.Debug {
		logLevel = slog.LevelDebug
	}

	if opts.JSON {
		log = slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: logLevel}))
	} else {
		log = slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: logLevel}))
	}

	if opts.Service != "" {
		log = log.With("service", opts.Service)
	}

	if opts.Version != "" {
		log = log.With("version", opts.Version)
	}

	return log
}