Proxy Certificate handling cleanup for public distribution

[mfarina1]

The inclusion of the APL-specific Proxy certificate (and internal url to fetch it) in the public repos is problematic. There's probably not a cleaner way to handle it, but at the very least, the URL should probably be moved into an ENV variable with APL-specific instructions providing the value to set it, and public instructions providing more generic information to help any users in other organizations with a similar setup.