Data API update (PR ensemble)

[Scitator]

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Description

Updated Config API:

      train:
        _target_: torch.utils.data.DataLoader
        dataset:
          _target_: MNIST
          root: *dataset_root
          train: True
          transform: &transform
            _target_: transform.Compose
            transforms:
              - _target_: transform.ToTensor
              - _target_: transform.Normalize
                mean: [0]
                std: [1]
          download: True
        batch_size: &batch_size 32
        sampler:
          _target_: MiniEpochSampler
          data_len: 50000
          mini_epoch_len: 35000
          drop_last: true
          shuffle: per_epoch
        num_workers: 1
      valid:
        _target_: DataLoader
        dataset:
          _target_: MNIST
          root: *dataset_root
          train: False
          transform: *transform
          download: True
        batch_size: *batch_size
        shuffle: false
        num_workers: 1
        drop_last: false

Related Issue

Type of Change

• Examples / docs / tutorials / contributors update
• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves an existing feature)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

FAQ

Please review the FAQ before submitting an issue:

• I have read the documentation and FAQ
• I have reviewed the minimal examples section
• I have checked the changelog for main framework updates
• I have read the contribution guide
• I have joined Catalyst slack (#__questions channel) for issue discussion

[mergify]

This pull request is now in conflicts. @Scitator, could you fix it? 🙏