Use CacheDataset for generative bundles.

[mingxin-zheng]

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

For the diffusion bundle, monai.apps.DecathlonDataset is used by the generative bundles.

https://github.com/Project-MONAI/model-zoo/blob/f9334c14dbd779898b4ec04ac2f72554b486a668/models/brats_mri_generative_diffusion/configs/train_autoencoder.json#L143

https://github.com/Project-MONAI/model-zoo/blob/f9334c14dbd779898b4ec04ac2f72554b486a668/models/brats_mri_axial_slices_generative_diffusion/configs/train_diffusion.json#L105

It provides some convenience (auto-downloading datasets), but it makes overwriting the input datalist more difficult. Can we replace it with CacheDataset like the other bundles, which have more flexibility?

Describe the solution you'd like Use CacheDataset for generative bundles.