Move the admin documentation to a new home

[beatrizserrano]

We need to move everything under https://galaxyproject.org/admin/ to https://docs.galaxyproject.org/en/master/admin/index.html.

@hexylena has kindly volunteered to do this after holidays :) Thank you, Helena!

[luigimorel]

hi @hexylena, how far with this?

[hexylena]

Hi @morelmiles it is not started yet. It's not a high priority issue, it'll probably happen by the summer and that's OK.