(doc): update documentation to match latest version of sight

Description

https://sight.pages.ircad.fr/sight-doc/HowTos/HowTo-DepsCreation.html#add-a-custom-dependency-repository

• The documentation still mentions sight-deps and the old way of managing dependencies. -> remove this part
• add missing description for tutos & samples
• Update linux version (21.04 & 21.10)