TF-2677 Create server settings capability & model

server_settings/lib/server_settings/converter/always_read_receipt_nullable_converter.dart

@@ -0,0 +1,19 @@
+import 'package:json_annotation/json_annotation.dart';
+
+class AlwaysReadReceiptNullableConverter implements JsonConverter<bool?, String?> {
+  const AlwaysReadReceiptNullableConverter();
+
+  @override
+  bool? fromJson(String? json) {
+    if (json == null) {
+      return null;
+    } else if (json == 'true') {
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  @override
+  String? toJson(bool? object) => object?.toString();
+}

server_settings/lib/server_settings/converter/server_settings_id_nullable_converter.dart

@@ -0,0 +1,13 @@
+import 'package:jmap_dart_client/jmap/core/id.dart';
+import 'package:json_annotation/json_annotation.dart';
+import 'package:server_settings/server_settings/server_settings_id.dart';
+
+class ServerSettingsIdNullableConverter implements JsonConverter<ServerSettingsId?, String?> {
+  const ServerSettingsIdNullableConverter();
+
+  @override
+  ServerSettingsId? fromJson(String? json) => json != null ? ServerSettingsId(id: Id(json)) : null;
+
+  @override
+  String? toJson(ServerSettingsId? object) => object?.id.value;
+}