Add datasets from training

[Lextuga007]

• NHSR Introduction to R and R Studio course https://github.com/nhs-r-community/intro_r_data/tree/26a2e39bd49d4aa95a8efc5b45c398386e6e4ed4
• RMarkdown course https://github.com/nhs-r-community/intro_rmd/tree/main/data

[tomjemmett]

I feel like there was a reason this wasn't done before? Having a quick look at the intro r datasets there are a few that aren't relevant to NHS-R (general country population files, there's probably already a package with this data?).

Of the datasets, the kh03 data possibly could be incorporated as a snapshot, like the A&E attendances. The A&E file looks like it's synthetic? I think it would be confusing to have two very similar datasets in the same package, so could the materials be adapted?