Base user workflow (create/update)

lib/api/model/user_model.dart

@@ -0,0 +1,27 @@
+class UserModel {
+  final int id;
+  final String username;
+  final String? password;
+  final String? accessToken;
+
+  UserModel({
+    required this.id,
+    required this.username,
+    this.password,
+    this.accessToken,
+  });
+
+  factory UserModel.fromJson(Map<String, dynamic> json) => UserModel(
+        id: json["id"],
+        username: json["username"],
+        password: json["password"],
+        accessToken: json["access_token"],
+      );
+
+  Map<String, dynamic> toJson() => {
+        "id": id,
+        "username": username,
+        "password": password,
+        "access_token": accessToken,
+      };
+}