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/core/Config.cpp

@@ -61,6 +61,7 @@ static const QHash<Config::ConfigKey, ConfigDirective> configStrings = {
     {Config::AutoSaveOnExit,{QS("AutoSaveOnExit"), Roaming, true}},
     {Config::AutoSaveNonDataChanges,{QS("AutoSaveNonDataChanges"), Roaming, true}},
     {Config::BackupBeforeSave,{QS("BackupBeforeSave"), Roaming, false}},
+    {Config::BackupFilePathPattern,{QS("BackupFilePathPattern"), Roaming, QString("{DB_FILENAME}.old.kdbx")}},
     {Config::UseAtomicSaves,{QS("UseAtomicSaves"), Roaming, true}},
     {Config::UseDirectWriteSaves,{QS("UseDirectWriteSaves"), Local, false}},
     {Config::SearchLimitGroup,{QS("SearchLimitGroup"), Roaming, false}},
@@ -229,6 +230,11 @@ QVariant Config::get(ConfigKey key)
     return m_settings->value(cfg.name, defaultValue);
 }
 
+QVariant Config::getDefault(Config::ConfigKey key)
+{
+    return configStrings[key].defaultValue;
+}
+
 bool Config::hasAccessError()
 {
     return m_settings->status() & QSettings::AccessError;