Add parameter to Upload to Zoltar action to switch between production and staging

[ydhuang28]

Right now to switch the upload script between production and staging one needs to commit the code/zoltar_scripts/upload_covid19_forecasts_to_zoltar.py script with STAGING = True to the master branch. To simplify this process, we should add a parameter to the GitHub action that runs this script to flip the variable from False to True.

Because the GitHub action does not call the python script directly, we need to make sure that the new parameter passes through the 2 shell scripts that eventually call the python script.