WIP settings system.

- updated dbdiagrams schema
- [BREAKING] force failure if `notify.filter_attributes` or `notify.level` is set
- added Settings table (and default values during migration)
- Added Save Settings and Get Settings functions.
- Added web API endpoints for getting and saving settings.
- Deprecated old Notify* constants. Created new MetricsStatus* and MetricsNotifyLevel constants.

webapp/backend/pkg/database/interface.go

@@ -28,4 +28,7 @@ type DeviceRepo interface {
 
 	GetSummary(ctx context.Context) (map[string]*models.DeviceSummary, error)
 	GetSmartTemperatureHistory(ctx context.Context, durationKey string) (map[string][]measurements.SmartTemperature, error)
+
+	GetSettings(ctx context.Context) (*models.Settings, error)
+	SaveSettings(ctx context.Context, settings models.Settings) error
 }