Create causal mask on MCore/TE side
@titu1994 could you help to land it? Prerequisite is mcore=0.5.0 https://github.com/NVIDIA/NeMo/pull/8465
# What does this PR do ?

Currently Megatron-LM creates causal attention mask for a local-layer spec model on its own -- see https://github.com/NVIDIA/Megatron-LM/commit/a45805a3ee0645b85b48d14b0a8077fa5b1216b2 -- and hence `attention_mask=None` can be specified in Nemo. In this MR, I'm using this new M-LM functionality when creating `fwd_output_only_func` function.

Broader functional tests for `fwd_output_only_func` will follow in subsequent MRs.

**Collection**: NLP

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# Additional Information
* Related to https://github.com/NVIDIA/Megatron-LM/commit/a45805a3ee0645b85b48d14b0a8077fa5b1216b2
