BUG: Update extension build system to report packaging error on CDash.
Created by: jcfr
See #3032
This commit adds a new target named "uploadpackage" that will (1) build the standard 'package' target, (2) extract the list of generated packages from its standard output and (3) append the list of generated package filepaths to a file named PACKAGES.txt, (4) upload the extension packages on midas.
Using this target an extension can be uploaded to midas without relying on CTest.
Within the ctest script, the target "uploadpackage" is built and then the URL to download packages from midas are uploaded to CDash based on the content of the file PACKAGES.txt
This commit removes the now obsolete ExperimentalUploadOnly target.