Develop spatial workshop SVGs submodule

This epic tracks work to develop the third spatial workshop submodule on spatially-variable genes.

Goals for this epic include:
- [ ] Outline instruction notebook, including the dataset to use
- [ ] Complete instruction notebook
- [ ] Outline exercise notebook, including the dataset to use
- [ ] Complete exercise notebook
- [ ] Maintain spatial module cheatsheet

Start by outlining the instruction notebook and choosing its dataset, then outline the exercise notebook and choose its dataset. The issue also calls for completing both notebooks and maintaining the spatial module cheatsheet; done means all five checklist goals are complete.

Written by the indexing model from the issue text.