Ensure auth config properties are pushed to UI from back-end

[EricWittmann]

The UI app should be configured with the keycloak server URL, realm, and other relevant configuration properties by having that information pushed to it via the dynamic config servlet:

https://github.com/Apicurio/apicurio-registry/blob/master/app/src/main/java/io/apicurio/registry/ui/servlets/ConfigJsServlet.java

This allows the auth configuration properties used by the API layer to be shared by the UI - we don't want to configure them separately.

This may already be working...

[EricWittmann]

This is a duplicate of #904 ... closing. GitHub UI broke when I was entering this issue and apparently it got added twice.