feat: add logic for the modrinth instance modpack page

Signed-off-by: flow <flowlnlnln@gmail.com>

launcher/modplatform/modrinth/ModrinthPackManifest.cpp

@@ -128,6 +128,7 @@ auto loadIndexedVersion(QJsonObject &obj) -> ModpackVersion
 
     file.name = Json::requireString(obj, "name");
     file.version = Json::requireString(obj, "version_number");
+    file.changelog = Json::ensureString(obj, "changelog");
 
     file.id = Json::requireString(obj, "id");
     file.project_id = Json::requireString(obj, "project_id");

launcher/modplatform/modrinth/ModrinthPackManifest.h

@@ -80,6 +80,7 @@ struct ModpackExtra {
 struct ModpackVersion {
     QString name;
     QString version;
+    QString changelog;
 
     QString id;
     QString project_id;