When Kubernetes mounts config maps onto volumes in a pod, it creates
hidden files on the pod filesystem with symbolic links to the
hidden files. The symlinks are named for the user-provided config
map that was mounted, while the hidden files have system-generated
names.

Prior to this commit, the property sources created by the
configtree property source were added to the environment using the
system-generated hidden file name instead of the user-provided
symlink name. This commit corrects that behavior so the property
sources are named as a user would expect.

Fixes gh-23232