ENH: Change Presence/Absence table to Frequency table in `annotate-mags-card` output

[VinzentRisch]

The action annotate-mags-card has a FeatureTable[Presence/Absence] as one output. But because one ARG can occur multiple times in one MAG, the information of the frequency is lost.
To account for this the output has to be changed to a FeatureTable[Frequency].