Bulk index CLI/task: support different record types/class

[ntarocco]

The RecordIndexer class accepts as optional param record_cls but the CLI and tasks do not and use the default Record class.
Such methods cannot be used with different record classes.

One possible solution would be to define a mapping rec type: rec class and pass the record type as extra param in CLI and tasks args.
See attempt to fix it in this wip PR.