add and render HistoryVisibilityContent

lib/models/content/history_visibility.dart

@@ -0,0 +1,19 @@
+import "package:freezed_annotation/freezed_annotation.dart";
+import "package:nexus/models/content/content.dart";
+part "history_visibility.freezed.dart";
+part "history_visibility.g.dart";
+
+@freezed
+abstract class HistoryVisibilityContent extends Content
+    with _$HistoryVisibilityContent {
+  HistoryVisibilityContent._();
+  factory HistoryVisibilityContent({
+    required HistoryVisibility historyVisibility,
+  }) = _HistoryVisibilityContent;
+
+  factory HistoryVisibilityContent.fromJson(Map<String, Object?> json) =>
+      _$HistoryVisibilityContentFromJson(json);
+}
+
+@JsonEnum(fieldRename: FieldRename.snake)
+enum HistoryVisibility { invited, joined, shared, worldReadable }