feat(datetime): Check availability of Auto Sync and indicate when it is not available

If systemd-timesyncd (Debian package name) is not installed on the user's computer,
set the option as unavailable and display a line of prompt text.

src/datetime/time.cpp

@@ -32,6 +32,8 @@ Time::Time(QObject *parent)
     OrgFreedesktopTimedate1Interface iface(QStringLiteral("org.freedesktop.timedate1"),
                                            QStringLiteral("/org/freedesktop/timedate1"),
                                            QDBusConnection::systemBus());
+
+    m_canNTP = iface.canNTP();
     m_useNtp = iface.nTP();
 }
 
@@ -40,6 +42,11 @@ bool Time::useNtp() const
     return m_useNtp;
 }
 
+bool Time::canNTP() const
+{
+    return m_canNTP;
+}
+
 void Time::setUseNtp(bool enabled)
 {
     if (m_useNtp != enabled) {

src/datetime/time.h

@@ -29,6 +29,7 @@ class Time : public QObject
 {
     Q_OBJECT
     Q_PROPERTY(bool useNtp READ useNtp WRITE setUseNtp NOTIFY useNtpChanged)
+    Q_PROPERTY(bool canNTP READ canNTP CONSTANT)
     Q_PROPERTY(QTime currentTime READ currentTime WRITE setCurrentTime NOTIFY currentTimeChanged)
     Q_PROPERTY(QDate currentDate READ currentDate WRITE setCurrentDate NOTIFY currentDateChanged)
     Q_PROPERTY(bool twentyFour READ twentyFour WRITE setTwentyFour NOTIFY twentyFourChanged)
@@ -37,6 +38,7 @@ public:
     explicit Time(QObject *parent = nullptr);
 
     bool useNtp() const;
+    bool canNTP() const;
     void setUseNtp(bool enabled);
 
     Q_INVOKABLE void save();
@@ -57,6 +59,7 @@ signals:
     void twentyFourChanged();
 
 private:
+    bool m_canNTP;
     bool m_useNtp;
     bool m_twentyFour;
     QTime m_currentTime;

src/qml/DateTime/Main.qml

@@ -64,11 +64,22 @@ ItemPage {
                         Layout.fillHeight: true
                         rightPadding: 0
                         rightInset: 0
+                        checkable: time.canNTP
                         checked: time.useNtp
                         onCheckedChanged: time.useNtp = checked
                     }
                 }
 
+                Label {
+                    text: qsTr("Unable to use Auto Sync. Please ensure your NTP service is installed.")
+                    color: FishUI.Theme.disabledTextColor
+                    visible: !time.canNTP
+                }
+            }
+
+            RoundedItem {
+                spacing: FishUI.Units.largeSpacing * 1.5
+
                 RowLayout {
                     Label {
                         text: qsTr("24-Hour Time")