Add example data to run scratch scripts for exponential growth rate analysis

[kaitejohnson]

Goal

Had written some test scripts to make exponential growth rate plots. These use real data, so can't put them on github but could create similar example data to be able to run the scripts with package data

Context

https://github.com/CDCgov/wastewater-informed-covid-forecasting/pull/167#discussion_r1771758947

[SamuelBrand1]

That would be nice. You've got a section on setting up api tokens etc so maybe have both?

[kaitejohnson]

We do already have example data too from the vignette. It's just not in this exact same format but can modify and save as example_input_data