Improve grammatical correctness and clarity of distro-specific error messages

CCBUG: 424100

discover/DiscoverObject.cpp

@@ -154,7 +154,10 @@ DiscoverObject::DiscoverObject(CompactMode mode, const QVariantMap &initialPrope
                 found |= b->hasApplications();
 
             if (!found)
-                Q_EMIT openErrorPage(i18n("No application back-ends found, please report to your distribution."));
+                Q_EMIT openErrorPage(
+                    i18n("Discover currently cannot be used to install any apps "
+                         "because none of its app backends are available. Please "
+                         "report this error to your distribution."));
         },
         this);
 

libdiscover/backends/PackageKitBackend/PackageKitNotifier.cpp

@@ -116,7 +116,7 @@ void PackageKitNotifier::checkOfflineUpdates()
             connect(trans, &PackageKit::Transaction::errorCode, this, [](PackageKit::Transaction::Error /*error*/, const QString &details) {
                 KNotification::event(QStringLiteral("OfflineUpdateRepairFailed"),
                                      i18n("Repair Failed"),
-                                     i18n("Please report to your distribution: %1", details),
+                                     xi18nc("@info", "%1<nl/>Please report this error to your distribution.", details),
                                      {},
                                      KNotification::Persistent,
                                      QStringLiteral("org.kde.discovernotifier"));