add org structure

model/organization.go

@@ -0,0 +1,10 @@
+package model
+
+import "gorm.io/gorm"
+
+type Organization struct {
+	gorm.Model
+	Name      string     `gorm:"unique;index"`
+	ParentID  uint       `json:"parent_id"`
+	Positions []Position `json:"positions,omitempty"`
+}