Changes for the 4.0.0 release of Dedicated User Environment

Licensing

All files have been updated with Nvidia copyright messages, to reflect
Nvidia's acquisition of Cumulus Networks.

New features

Support for Red Hat and SUSE based containers, with an RPM duebuild
script.
Support for running on Red Hat, SUSE, and Windows Subsystem for Linux
hosts.

Added --run --entrypoint override option to allow for interactive
container debug.
Added --run --platform to specify the architecture of the Docker image.

Image builds now use a directory inheritance model to reduce file
duplication.
Image build targets can be put in to sub directories, such that files in
the parent directories are shared among build targets, and files in
lower directories can overwrite them to create a particular image. The
rhel-package and fedora-package targets building with a common duebuild
script for RPMs in the file system directory under the templates/redhat
directory is an example of this.

The user's ~/.config/due/due.conf can have customized default arguments
for container launch, if the sysadmin allows it. Always mounting a
particular host directory when running a container would be one example
of how this saves typing.

Internal build

Makefile supports Debian packaging on debian/master or debian-test.
Makefile adds conditional logic to be inactive during package build.

Documentation updates

FAQ.md - added for RPM/Podman references.
Docs - updated Building.md.
Troubleshooting.md - mentioned systemd-binfmt to close out Issue #39.
docs/DUEAndWSL.md - Initial commit to document issues found during
install.
Added Release Notes directory to elaborate on changes.

Runtime

Due now prints sourced file paths if DUE is being run locally, for
clarity.
due-bashrc now does not export $PS1 any more, as that could cause
inconsistent behavior.
pipefail was added to identify the source of a failure.
