Add CropHarvest Dataset

[GeorgeHuber]

Draft PR to add cropharvest dataset to torchgeo.

• Implement the dataset extending either GeoDataset or NonGeoDataset
• Add the dataset definition to torchgeo/datasets/init.py
• Add a data.py script to tests/data// that generates test data with the same directory structure/file naming conventions as the new dataset
• Add appropriate tests with 100% test coverage to tests/datasets/
• Add the dataset to docs/api/datasets.rst
• Add the dataset metadata to either docs/api/geo_datasets.csv or docs/api/non_geo_datasets.csv

Sample plot for single pixel timeseries over 12 months:

[calebrob6]

Thanks for the contribution @GeorgeHuber! Let me know if you want help with the linting / mypy (you can read more about it here https://torchgeo.readthedocs.io/en/latest/user/contributing.html#linters)

[adamjstewart]

Almost finished! Just a couple typo fixes and questions left.