Allow using same asset server for all deployments

[maxpatiiuk]

The deployed test panel had its source code modified a bit to use the same asset server for all deployments (as well as to support report fonts if I remember correctly)

We should clean this up to instead add a config option for this, and have credentials come from an environment variable. See https://nextjs.org/docs/pages/building-your-application/configuring/environment-variables

Also see https://specifydev.slack.com/archives/C05B9HEUE6L/p1689618778928559