Add additional environment variables for sensitive information

[kenlasko]

I see there is already support for USERS_SERVERADMIN_EMAIL and USERS_SERVERADMIN_PASSWORD as environment variables. This should be extended to other potentially sensitive things such as:

• email.smtp_host
• email.smtp_user
• email.smtp_pass
• server.secret

Others may have additional settings as well.

Ideally, this should be done in conjunction with #749 to support Docker Secrets. This will allow me to store the entire config in a Git repo without sharing secrets.

[kinouzero]

And the postgres connection string as well

[oschwartz10612]

Postgres string will be available in the 1.11.0 release this week from db513b4. The email password is already available as an env var EMAIL_SMTP_PASS. I think we are going to close this as completed!