Consider loading url locations from config file.

[Michael Aldridge]

When packaging the dashboard as a distribution level file, the envsubst workflow that docker uses, while clever, does not work. Most distributions will consider that a modified file and then subsequently either overwrite it or if it was declared as a config file, refuse to modify it on update.

It would be great if a request would be made to the location the bundle was loaded from to a path such as /dashboard/config.json which could be provided by a site operator that would provide the URLs necessary to point back to the self hosted admin service. If such a file is loadable, its URLs should be used rather than those that are baked into the bundle.