[New Environment Setup] Simplify password setup

[esoergel]

In the new environment setup, users are instructed to manually create a bunch of passwords here. There's no need for this to be done manually.

This should be automated, for instance using a "start new project" script, analogously to Django's startproject. As a reference point, startproject autogenerates SECRET_KEY using a utility, get_random_secret_key(). Ensure generated usernames use a legal character set for the places they'll be used.

https://dimagi-dev.atlassian.net/browse/SC-299