Spectral representation in SMF table

[YasinEl]

Hello, and thank you for maintaining this tool!

We propose adding a “MSn_representative_spectrum” column to the SMF table. This would allow to add an MSn scan ID (as e.g. ms_run[x]:123 with 123 being the scan ID in the mzML file or spectral_representation[x]:123 when using a spectra collection as proposed in #222)