chore(settings): refactor settings processing (#756)

- Better settings tree structure logged using `qdm12/gotree`
- Read settings from environment variables, then files, then secret files
- Settings methods to default them, merge them and override them
- `DNS_PLAINTEXT_ADDRESS` default changed to `127.0.0.1` to use DoT. Warning added if set to something else.
- `HTTPPROXY_LISTENING_ADDRESS` instead of `HTTPPROXY_PORT` (with retro-compatibility)

internal/dns/state/settings.go

@@ -4,23 +4,23 @@ import (
 	"context"
 	"reflect"
 
-	"github.com/qdm12/gluetun/internal/configuration"
+	"github.com/qdm12/gluetun/internal/configuration/settings"
 	"github.com/qdm12/gluetun/internal/constants"
 )
 
 type SettingsGetSetter interface {
-	GetSettings() (settings configuration.DNS)
+	GetSettings() (settings settings.DNS)
 	SetSettings(ctx context.Context,
-		settings configuration.DNS) (outcome string)
+		settings settings.DNS) (outcome string)
 }
 
-func (s *State) GetSettings() (settings configuration.DNS) {
+func (s *State) GetSettings() (settings settings.DNS) {
 	s.settingsMu.RLock()
 	defer s.settingsMu.RUnlock()
 	return s.settings
 }
 
-func (s *State) SetSettings(ctx context.Context, settings configuration.DNS) (
+func (s *State) SetSettings(ctx context.Context, settings settings.DNS) (
 	outcome string) {
 	s.settingsMu.Lock()
 
@@ -31,8 +31,8 @@ func (s *State) SetSettings(ctx context.Context, settings configuration.DNS) (
 	}
 
 	// Check for only update period change
-	tempSettings := s.settings
-	tempSettings.UpdatePeriod = settings.UpdatePeriod
+	tempSettings := s.settings.Copy()
+	*tempSettings.DoT.UpdatePeriod = *settings.DoT.UpdatePeriod
 	onlyUpdatePeriodChanged := reflect.DeepEqual(tempSettings, settings)
 
 	s.settings = settings
@@ -45,7 +45,7 @@ func (s *State) SetSettings(ctx context.Context, settings configuration.DNS) (
 
 	// Restart
 	_, _ = s.statusApplier.ApplyStatus(ctx, constants.Stopped)
-	if settings.Enabled {
+	if *settings.DoT.Enabled {
 		outcome, _ = s.statusApplier.ApplyStatus(ctx, constants.Running)
 	}
 	return outcome