Convert db backend to use Gorm, with basis for support

for Mysql and Postgres in addition to existing Sqlite

backend/internal/entity/model_base.go

@@ -0,0 +1,13 @@
+package entity
+
+import (
+	"gorm.io/plugin/soft_delete"
+)
+
+// ModelBase include common fields for db control
+type ModelBase struct {
+	ID        uint                  `json:"id" gorm:"column:id;primaryKey"`
+	CreatedAt int64                 `json:"created_at" gorm:"<-:create;autoCreateTime:milli;column:created_at"`
+	UpdatedAt int64                 `json:"updated_at" gorm:"<-;autoUpdateTime:milli;column:updated_at"`
+	DeletedAt soft_delete.DeletedAt `json:"-" gorm:"column:is_deleted;softDelete:flag"`
+}