drop into shell with full environment in case of failure

[surak]

This is an issue regarding the discussion on 19.01.2022

[boegel]

We're looking into implementing support for this in EasyBuild 5.0, along with the implementation of the new run function (see #4252).

@Micket mentioned he has looked into this a bit already, but it would be good to get #4284 merged first to start working on the actual implementation (which probably involves leveraging pty.spawn)

[boegel]

Starting an interactive shell for a failing shell command will be supported in EasyBuild 5.0, see #4486, so closing this...