Similarly to rf_mode, previously type of emulated UE was static parameter of
particular software release - it was possible to simulate UE and attach to
cells only of the RAT of particular template.

In MultiRU it will be possible to generally emulate all kind of UEs - both LTE
and NR all at the same time, and attach them to LTE and NR cells
simultaneously.

-> Switch type of UE to be runtime parameter as a preparatory step for that.

URLs of software releases changes again (we remove lte and nr in names), but
here we do not care about backward compatibility because currently there is just
a few UEsim deployments and migration should be easy.