added user signup feature

internal/api/dto.go

@@ -5,3 +5,8 @@ type bookPostCreate struct {
 	Author string `json:"author" binding:"max=100"`
 	Rating int    `json:"rating" binding:"min=0,max=10"`
 }
+
+type userPostCreate struct {
+	Username string `json:"username" binding:"required,min=2,max=20"`
+	Password string `json:"password" binding:"required,min=6,max=100"`
+}