Set up Auth0 for staging

[macfarlandian]

What needs to be done? Why does it need to be done?
We need to have a private staging environment so that we can deploy pre-release builds without having them openly available on the internet. To accomplish this we should:

• create a new Auth0 tenant
• configure it similarly to the staging tenant for pulse-dashboard, whitelisting only recidiviz.org emails
• allow it to be toggled with an envvar at build time (on for staging, off for prod by default)
• put the entire site behind this optional auth check