Review / Update Data styling and architecture section of docs

[ljowen]

https://docs.terria.io/guide/connecting-to-data/customizing-data-appearance/overview/ and https://docs.terria.io/guide/contributing/architecture/ may have out of date examples.

We need to do a review that any API changes from v7 -> v8 are reflected in the documentation and where possible enhance the documentation with examples, screenshots, share links, etc.