Add Galaxy version information to the GTN admin materials

[hechth]

Currently it is quite difficult to figure out whether a feature covered in the admin training is actually supported by a Galaxy version and I think some info in the beginning of the admin training saying which galaxy version this training is targeting would be very useful.

[hexylena]

Generally you can check the ansible-galaxy tutorial for what the 'current' version is. Would you expect this on every GAT tutorial?

[hexylena]

@hechth if you have more input on this let me know :) (just where you would expect to see a notice/which tutorials/etc.)