Trainers tutorial: switch dataset

[adamjstewart]

Summary

We should switch the dataset for our PyTorch Lightning Trainers tutorial.

Rationale

Our current dataset is downloaded from Radiant Earth, requiring additional dependencies and preventing users from running the tutorial without first signing up for an account and modifying the notebook. It would be better to use a dataset that does not require these things so that the tutorial works out of the box.

Implementation

Most of our other current tutorials use EuroSAT, so we could use that.

Alternatives

Should we just choose the smallest and fastest to download dataset and use that for all tutorials?

Additional information

No response

[adamjstewart]

Another benefit: secrets aren't shared with unprivileged actors, so our tutorials tests fail when anyone other than a maintainer opens a PR that modifies the notebooks. By switching to a public dataset, the tests will always work.