Add PBS Scheduler Support

**Is your feature request related to a problem? Please describe.**

While NeMo-RL provides excellent [Slurm documentation](https://docs.nvidia.com/nemo/rl/latest/cluster_start.html) and examples, there's no equivalent support for PBS environments. The main challenge is Nemo RL's dependency on Ray, which is difficult to configure and use effectively in PBS environments, even when it's technically possible to get it working. This creates a significant barrier for researchers who want to use it on academic clusters.

**Describe the solution you'd like**

I would like PBS-specific documentation and examples similar to what exists for Slurm or an even better approach would be a path that doesn't depend on Ray.

**Describe alternatives you've considered**

- **Manual Ray setup** - Tried configuring Ray manually on PBS but ran into issues with node discovery and resource allocation
- **In-framework execution path** - An alternative solution could be developing a Megatron based execution path that doesn't rely on Ray