Add API to nullify log_data

[palkan]

Sometimes it might be necessary to reset the history for a record (or records) (e.g. with some GDPR-related stuff).

Let's add an API to do that. Something like this:

# for single record
record.reset_log_data #=> which is, probably, equal to Logidze.without_logging { record.update_column(:log_data, nil) }

# for relation
User.where(...).reset_log_data #=> Logidze.without_logging { relation.update_all(log_data: nil) }

[Arkweid]

Take this one

[Arkweid]

@palkan opened: #110

[palkan]

Closed by #110