Update Dask notebook with additional content from DE Africa ⚙

[robbibt]

We have a Dask notebook in the Beginners_guide here: https://docs.dea.ga.gov.au/notebooks/Beginners_guide/09_Parallel_processing_with_Dask.html

However, DE Africa has also recently added several more detailed guides here:
https://github.com/digitalearthafrica/deafrica-docs/tree/main/sandbox/dask-howto

We should investigate how this content could be re-used in DEA so that users can get training on using Dask for parallel processing and scaling up their workflows.