[Feature] Support dumping datasets to pkl file

[jbwang1997]

What's the feature?

Suggest adding a dump function to BaseDataset. This function will make the dataset more flexible. Users can first dump the dataset to a pkl file, and then reformat its structure to anther dataset type.

Users can dump the dataset like this:

dataset.dump('data_list.pkl')

Then, data_list can also be directly loaded

dataset.load('data_list.pkl')

Any other context?

No response

[RangiLyu]

I think maybe the BaseDataset in mmengine can support a dumping function.

[jbwang1997]

I can support a dump function to save all data in self.data_list into a .pkl file.

And I also suggest supporting dataset wise dump functions to format self.data_list into the certain dataset format. It will benefit many dataset operations like transformation, separation.