Set env var ARDUINO_MODE to "cli" or "daemon"

Depending on how the arduino-cli is run, the tools may decide to show a
GUI or print their output on terminal.

cli/cli.go

@@ -45,6 +45,7 @@ import (
 	"github.com/arduino/arduino-cli/cli/upload"
 	"github.com/arduino/arduino-cli/cli/version"
 	"github.com/arduino/arduino-cli/configuration"
+	"github.com/arduino/arduino-cli/executils"
 	"github.com/arduino/arduino-cli/i18n"
 	"github.com/arduino/arduino-cli/inventory"
 	"github.com/fatih/color"
@@ -157,6 +158,9 @@ func parseFormatString(arg string) (feedback.OutputFormat, bool) {
 func preRun(cmd *cobra.Command, args []string) {
 	configFile := configuration.Settings.ConfigFileUsed()
 
+	// Initialize env for spawned processes
+	executils.SetProcessGlobalEnv([]string{"ARDUINO_MODE=cli"})
+
 	// initialize inventory
 	err := inventory.Init(configuration.Settings.GetString("directories.Data"))
 	if err != nil {

cli/daemon/daemon.go

@@ -30,6 +30,7 @@ import (
 	"github.com/arduino/arduino-cli/cli/globals"
 	"github.com/arduino/arduino-cli/commands/daemon"
 	"github.com/arduino/arduino-cli/configuration"
+	"github.com/arduino/arduino-cli/executils"
 	"github.com/arduino/arduino-cli/i18n"
 	"github.com/arduino/arduino-cli/metrics"
 	srv_commands "github.com/arduino/arduino-cli/rpc/cc/arduino/cli/commands/v1"
@@ -70,6 +71,8 @@ func NewCommand() *cobra.Command {
 func runDaemonCommand(cmd *cobra.Command, args []string) {
 	logrus.Info("Executing `arduino-cli daemon`")
 
+	executils.SetProcessGlobalEnv([]string{"ARDUINO_MODE=daemon"})
+
 	if configuration.Settings.GetBool("metrics.enabled") {
 		metrics.Activate("daemon")
 		stats.Incr("daemon", stats.T("success", "true"))