Optional metadata CV Term for custom retention time calculation

[nilshoffmann]

In lipidomics (LDA), there exists a use case to calculate a custom retention time, weighted by peak areas to distinguish closely eluting peaks of different molecular species, where one mol. species may occur in both peaks.

This could be covered by an optional CV Term in the metadata section: retention_time_summary_function that could take on values "native", "adjusted retention time" (e.g. after alignment), "peak area weighted", ...