Fix the dictionary  format returned by the `scheduler` method
# What does this PR do ?

I am changing the dict format returned by `scheduler` method in the new `lightning/optim` module. 

I followed the example of `LRSchedulerModule` to create a custom cosine annealing scheduler. My scheduler was returning the dict format: 
```
        return {
            "optimizer": optimizers,
            # REQUIRED: The scheduler instance
            # `interval` is the unit of the scheduler's step size, could also be 'step'.
            # 'epoch' updates the scheduler on epoch end whereas 'step'
            # updates it after a optimizer update.
            "scheduler": lr_scheduler,
            "interval": self.interval,
             "frequency": self.frequency,
            # Metric to monitor for schedulers like `ReduceLROnPlateau`
            "monitor": self.monitor,
        }
```

With this format, I was getting a warning: 
```
[NeMo W 2024-07-03 16:27:38 nemo_logging:349] /usr/local/lib/python3.10/dist-packages/pytorch_lightning/core/optimizer.py:376: Found unsupported keys in the optimizer configuration: {'scheduler', 'frequency', 'interval'}
```
and the learning rate was not decreasing (which is wrong)

changing it to the following format fixed the issue: 
```
        return {
            "optimizer": optimizers,
            # REQUIRED: The scheduler instance
            # `interval` is the unit of the scheduler's step size, could also be 'step'.
            # 'epoch' updates the scheduler on epoch end whereas 'step'
            # updates it after a optimizer update.
            "lr_scheduler": {
                "scheduler": lr_scheduler,
                "interval": self.interval,
                "frequency": self.frequency,
            },
            # Metric to monitor for schedulers like `ReduceLROnPlateau`
            "monitor": self.monitor,
        }
```

![image](https://github.com/NVIDIA/NeMo/assets/17721108/186599df-8ab1-4c74-8848-1896aaf0b13e)

**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.


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# Additional Information
* Related to # (issue)
