question: How to access `LightningDataModule` in `LightningModule`
context: In TorchGeo, we use PyTorch Lightning to organize reproducible benchmarks for geospatial datasets. Currently, we have a set of LightningDataModules for each dataset and a much smaller number of LightningModules for each task (semantic segmentation, classification, regression, etc.). Each Dataset defines its own plot() method that describes how to plot images and masks.
  During training/validation steps, we would like to plot a few examples to see how training is progressing. However, the LightningModule doesn't seem to know anything about the LightningDataModule/DataLoader/Dataset. Because of this, if we want to perform dataset-specific plotting during training or validation steps, we're forced to create a separate LightningModule for each dataset, increasing code duplication and defeating the whole purpose of PyTorch Lightning (example).
  Is there an easy way for a LightningModule to tell which DataModule/DataLoader/Dataset is being used and call its dataset.plot() method?
  @calebrob6 @isaaccorley
  @tchaton this is slightly related to #10469 but different enough that I wanted to start a separate discussion about it.
answer: @adamjstewart There is a reference to datamodule via trainer from LightningModule, but would that solve your issue?
  self.trainer.datamodule