add r-cookbook examples to visual test suite

we're adding a lot of functionality based off the r-coobook examples, so I thought I'd just add them to our visual-diffing test suite
This whole header doesn't make sense in a test suite.
Wrap `py <- plotly("ggplot2-cookbook", "gzcn4660jr")` in a function like we did in `run_tests_with_outputs.R`.
We could also define `py2 <- plotly("ggplot2-cookbook", "gzcn4660jr")` alongside `py` if we are using both accounts in the same script or function calls.