[ENHANCEMENT] Context Parallel Support for Mamba2

**Is your feature request related to a problem? Please describe.**
Megatron LM currently supports context parallelism (CP) for GPT-based models, but it does not look like CP is supported for Mamba2 models.

**Describe the solution you'd like**
It would be great to extend CP support to Mamba2 SSM layers.

**Describe alternatives you've considered**
We have used other forms of parallelism, such as tensor, pipeline, and sequence to train Mamba-based models, but context parallelism is lacking and could be very useful for certain applications such as DNA sequence modeling.

**Proposed implementation**
A possible solution for extending CP support to Mamba has been proposed in the mamba_ssm repository: https://github.com/state-spaces/mamba/pull/664