Add support for the faithfuld dataset in ggplot2

[tikkss]

https://ggplot2.tidyverse.org/reference/faithfuld.html

Maybe unavailable csv file:
https://github.com/tidyverse/ggplot2/blob/57ba97fa04dadc6fd73db1904e39a09d57a4fcbe/data-raw

License: CC0-1.0

https://community.rstudio.com/t/licenses-for-data-in-tidyverse/129334/7

I actually asked hadley about the datasets, and basically his stance
is that all datasets should be CC0. So, if you want to cite something,
cite the package, or just cite the dataset as CC0.

[tikkss]

tidyverse/ggplot2#6105

because I see no need within the R ecosystem for ggplot2 to explicitly export these datasets as csv file, and it is straightforward to export them if so needed.