title: Mongo-go-driver get objectID from insert result
body: <p>After using <code>InsertOne</code> to create a new document, when I return the result I'm getting an array of numbers rather than an <code>ObjectID</code>. In the DB, the id is generating fine. </p>
  
  <pre><code>type User struct {
    ID       string
    Email    string
    Username string
    Password string
  }
  
  var db = ...
  
  // UserStore creates user
  func UserStore(c echo.Context) (err error) {
  
    coll := db.Collection("users")
  
    u := new(User)
    if err = c.Bind(u); err != nil {
      return c.JSON(http.StatusInternalServerError, err)
    }
  
    result, err := coll.InsertOne(
      context.Background(),
      bson.NewDocument(
          bson.EC.String("email", u.Email),
          bson.EC.String("username", u.Username),
          bson.EC.String("password", u.Password),
      ),
    )
    if err != nil {
      return c.JSON(http.StatusInternalServerError, err)
    }
  
    return c.JSON(http.StatusCreated, result)
  }
  </code></pre>
  
  <p>This returns something like <code>InsertedID: [90, 217, 85, 109, 184, 249, 162, 204, 249, 103, 214, 121]</code> instead of a normal <code>ObjectID</code>. How can I return the actual <code>ObjectID</code> from the newly inserted document?</p>