Support remote database access using external tools (#7222)

* Provide remote database sync capability

Allow arbitrary commands to be defined and executed for syncing databases with remote services. This includes sftp, scp, rsync, etc. 

Remote commands are stored per-database and sync operations are manually triggered by the user from the Database -> Remote Sync menu. 

---------

Co-authored-by: Stefan Forstenlechner <t-h-e@users.noreply.github.com>
Co-authored-by: Jonathan White <support@dmapps.us>

tests/mock/MockRemoteProcess.cpp

@@ -0,0 +1,56 @@
+/*
+ *  Copyright (C) 2023 KeePassXC Team <team@keepassxc.org>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 2 or (at your option)
+ *  version 3 of the License.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <QFile>
+
+#include "MockRemoteProcess.h"
+
+MockRemoteProcess::MockRemoteProcess(QObject* parent, const QString& dbPath)
+    : RemoteProcess(parent)
+    , m_dbPath(dbPath)
+{
+}
+
+void MockRemoteProcess::start(const QString&)
+{
+    QFile ::copy(m_dbPath, m_tempFileLocation);
+}
+
+qint64 MockRemoteProcess::write(const QString& data)
+{
+    return data.length();
+}
+
+bool MockRemoteProcess::waitForBytesWritten()
+{
+    return true;
+}
+
+void MockRemoteProcess::closeWriteChannel()
+{
+    // nothing to do
+}
+
+bool MockRemoteProcess::waitForFinished(int)
+{
+    return true; // no need to wait
+}
+
+int MockRemoteProcess::exitCode() const
+{
+    return 0; // always return success
+}