Implement `fermi energy` output and `fixed total magnetization`

[t-reents]

In #344, support for fixing the total magnetization was added. Moreover, we added the fermi energy as an optional output, as this is used by the EnergyMagnetizationWorkChain.

This issue is used to keep track of implementing those changes also for the different plugins, as this is currently only done for AiiDA-QE.