Allow admin email to be specified via ADMIN_EMAIL param

Currently, the admin account is created with a generated email. In certain use cases, i.e. SSO, we would need to define this admin email to a specific value. However, because there is no parameter to allow us to specify this, the account will need to be updated after it was created.

There should be a way of specifying this in the template so that the account doesn't need to be updated after it was already created. There is an env var used to seed this admin account. The ADMIN_EMAIL parameter should point to this.