Allow specifing database backup paths. (#7035)

- Default backupFilePath is '{DB_FILENAME}.old.kdbx' to conform to existing standards
- Implement backupPathPattern tests.
- Show tooltip on how to format database backup location text field.

src/cli/Create.cpp

@@ -165,7 +165,7 @@ int Create::execute(const QStringList& arguments)
     }
 
     QString errorMessage;
-    if (!db->saveAs(databaseFilename, Database::Atomic, false, &errorMessage)) {
+    if (!db->saveAs(databaseFilename, Database::Atomic, QString(), &errorMessage)) {
         err << QObject::tr("Failed to save the database: %1.").arg(errorMessage) << endl;
         return EXIT_FAILURE;
     }