TF-56 Implement upload single attachment

lib/features/composer/domain/state/upload_attachment_state.dart

@@ -0,0 +1,27 @@
+import 'package:core/core.dart';
+import 'package:model/model.dart';
+
+class UploadAttachmentLoadingState extends UIState {
+  UploadAttachmentLoadingState();
+
+  @override
+  List<Object?> get props => [];
+}
+
+class UploadAttachmentSuccess extends UIState {
+  final Attachment attachment;
+
+  UploadAttachmentSuccess(this.attachment);
+
+  @override
+  List<Object?> get props => [attachment];
+}
+
+class UploadAttachmentFailure extends FeatureFailure {
+  final exception;
+
+  UploadAttachmentFailure(this.exception);
+
+  @override
+  List<Object> get props => [exception];
+}