Add FDO_UPSTREAM_REGISTRY to specify registry path

This adds a new variable that complements FDO_UPSTREAM_REPO. It will default to whatever FDO_UPSTREAM_REPO is set to but turned into lower case, as that is usually where the container image registry is located it for a project.

It is still possible to set the FDO_UPSTREAM_REGISTRY when using the templates, to override the derived default.

Closes: #22 (closed)

Signed-off-by: Jonas Ådahl jadahl@gmail.com