Add Mcore microbatches calculator supports
This PR is an replacement of https://github.com/NVIDIA/NeMo/pull/9838 due to signoff issue. Adding decreasing related support in separate PR later  Besides the comment about the in-line imports, LGTM @terrykong This is actually an legacy setting inherited from previous version. They use try except to avoid import error and use 
```
if not HAVE_MEGATRON_CORE:
            logging.warning(
                "megatron-core was not found. Please see the NeMo README for installation instructions: https://github.com/NVIDIA/NeMo#megatron-gpt."
            )
```
to log warnings. I am thinking try to avoid this part and log a version warning for not able to use mcore mb calculator like:
```
try:
    from megatron.core.num_microbatches_calculator import get_num_microbatches

except (ImportError, ModuleNotFoundError):
    logging.warning("megatron-core num_microbatches_calculator not found, using Apex version.")
    from apex.transformer.pipeline_parallel.utils import get_num_microbatches
```
# What does this PR do ?

Add Mcore microbatches calculator supports. Added backward compatibility. Merged `init_num_mb_calculator` and `reconfigure_num_mb_calculator`

**Collection**: [Note which collection this PR will affect]

# Changelog 
- Add specific line by line info of high level changes in this PR.

# Usage
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```python
# Add a code snippet demonstrating how to use this 
```

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