Can't use preauthenticated mode while running Docker images.

[gargrag]

Since the entry point overrides the file rundeck-config.properties it's not useful to mount a custom file, and there're no mapped env variables for configuring this feature.

Also, the documentation is wrong, since version 3.0, editing the file WEB-INF/web.xml inside the rundeck.war is not needed, and the file does not exist anymore, as explained on the changelog for version 3.0.0

I have created a PR on the documentation, to remove the part of "modifying the web.xml file" here