Add IAM scaffold modules

iam/internal/repo/user_store.go

@@ -0,0 +1,20 @@
+package repo
+
+type User struct {
+	ID   int64
+	Name string
+}
+
+type UserStore interface {
+	FindByID(id int64) (*User, error)
+}
+
+type inMemoryUserStore struct{}
+
+func NewInMemoryUserStore() UserStore {
+	return &inMemoryUserStore{}
+}
+
+func (s *inMemoryUserStore) FindByID(id int64) (*User, error) {
+	return &User{ID: id, Name: "demo"}, nil
+}