Improve validations for `docknext` scripts

[d3p1]

Description

The validation before execution of the docknext init, docknext mage-install, docknext mage-setup and docknext ide-setup commands could be improved.

Solution

Improve validation before execution of the docknext init, docknext mage-install, docknext mage-setup and docknext ide-setup commands.

Additional information

• docknext init
• docknext mage-install
• docknext mage-setup
• docknext ide-setup