[ENH] update_complex_name to handle real+imaginary complex data

[bpinsard]

Someone recently shared with me some GE Hyperband multi-echo data from a SIGNA UHP, where they exported mag + real + imaginary data (weird combination but why not), all 3 ends up in the same series. So that should ideally be handled in heudiconv within update_complex_name which only covers mag+phase case for now.

Though I hope it won't be the final export format for that project, it could make sense to cover that usecase in heudiconv.

I don't know if there are any open test data with real+imaginary data within the same series, @neurolabusc ?