Ability to list which e2e versions have tests embedded

[johnSchnake]

When figuring out which versions are supported for sonobuoy e2e you have to come to github and know where to look. It would be better to be able to dump the embedded versions via a command sonobuoy e2e versions or flag sonobuoy e2e --supported-versions.

There can be a difference between the online and offline modes so lets take that into consideration. This can allow us to store the test lists on github for N versions but not have to embed them all into the binary and make it bloat over time.