Add support for replicated shard strategy for tarred datasets
As in remove the configs shard_strategy = scatter portion? We could drop them, but it reduces visibility. Practically, it should be fine, since the shard strategy is not used unless is_tarred is set 

Edit: I do agree that the configs are going quite big though.  I was worried about it potentially causing some confusion, since it's not explicitly named in relation to the tarred dataset. How do you feel about a `null` option like for `tarred_audio_filepaths` when `is_tarred` is False? Oh that's a good option. None by default switches to the current scatter strategy and otherwise the user sets it explicitly. I'll make the changes  Another is to name the parameter `tarred_shard_strategy`  Either sounds good to me Thanks !
# Changelog
- Support `replicate` strategy for sharding of tarfiles under ddp for Tarred WebDataset.
- Add config line to all ASR models

Signed-off-by: smajumdar <titu1994@gmail.com>