east should force nrfutil toolchain manager to use the correct nrfutil internally

[TjazVracko]

Context

Currently when a command using the nrfutil runs inside the nrfutil toolchain-manager environmentthe actualnrfutilthat is used is the one provided by the system (found onPATH) and not the one that is downloaded/used by the east (on path ~/.local/share/east/tooling/nrfutil/nrfutil` ).

This should be changed, as it would make it easier for to ensure that correct version of nrfutil is used.

Definition of Done

Running command east bypass -- which nrfutil returns ~/.local/share/east/tooling/nrfutil/nrfutil .