Report missing tables in import metrics

[mdoering]

When reviewing imports it is good to know about what source files were included or are missing. This highly depends on the data format. Consider to include a report on all existing and important missing tables in the import metrics.

The list of existing tables could easily be extracted dynamically from the verbatim data. It might even be useful to know which terms/columns have been used, i.e. contained at least some data in some record (as opposed to columns that are always empty).

The current metrics already contain the distinct existing source tables with records counts. See pie chart at the bottom right: Afrotropical Bees DwC: https://www.col.plus/dataset/2035/metrics Fishbase ACEF: https://www.col.plus/dataset/1010/metrics missing AcceptedInfraSpecificTaxa

[mdoering]

With the list of existing tables/source files already shown in import metrics this is not needed