upgrade PTL trainer flags
Signed-off-by: nithinraok <nithinrao.koluguri@gmail.com>

# What does this PR do ?

Upgrade pytorch_lightning trainer flags that are going to be deprecated in future

**Collection**: Core and All collections yaml files 

# Changelog 
- Update pytorch_lightning deprecated variables, namely:

> -  accelerator to the trainer now takes the type of accelerator device than distributed type
> -  distributed type is handled by strategy flag
> -  previously: accelerator='ddp' now accelerator='gpu' strategy='ddp'
> -  trainer flag checkpoint_callback is renamed to enable_checkpointing
> - ModelCheckpoint argument evert_n_val_epochs renamed to every_n_epochs
> - Update `trainer.gpus` to `trainer.devices` ( With this change setting devices=0 doesnt auto select gpu instead need to make accelerator='cpu' and also note accelerator=cpu now will only accept >0 as values for devices) 
> - `examples/asr/transcribe_speech.py` script modified to remove cuda option. Script automatically searches for GPU and if its not present then falls back to CPU  
> - `checkpointing_callback` -> `enable_checkpointing` 
> - `flush_logs_every_n_steps` removed from trainer flags
> - `sync_batchnorm` and `num_nodes` removed from NLPDPPPlugins 

# Usage
- 

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# Additional Information
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