feat: add mod update check tasks

Those tasks take a list of mods and check on the mod providers for
updates. They assume that the mods have metadata already.

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

launcher/modplatform/ModIndex.h

@@ -54,6 +54,7 @@ struct IndexedVersion {
     QVariant addonId;
     QVariant fileId;
     QString version;
+    QString version_number = {};
     QVector<QString> mcVersion;
     QString downloadUrl;
     QString date;