Feature Request: Make ASSETS_URL optional

[andreicioromila]

ASSETS_URL is currently required in order to serve the frontend application for schema registry. However, it is only used inside the HTML page for the frontend. If omitted, browsers would just load the assets from the same host that the user is on.

I am not sure what use case is covered by setting it, but I think the default should be that assetsRootURL is undefined and the browser tries to load just href="/assets/management-ui-standalone.css?v=${assetsVersion}"

[jon-frankel]

I found setting ASSETS_URL to . works fine. An empty string will cause it to fall back on localhost:6001 but . will cause it use ./assets/management... which does work.