Ability to tag datasets that have been imported via etl

[spoonerf]

Core problem

Typically our datasets and charts are tagged with a topic and then all of the datasets and charts of a given topic can be viewed together e.g. here. It is useful to be able to see all the charts and datasets of a given topic together and will be especially useful as we go through all the topic page redesigns.

Currently it is not possible to tag a dataset that has been imported via etl or importers. There are 597 such datasets, listed here.

Proposed solution

Allow for the tagging of all datasets, regardless of their input method. However, I am not certain how possible or easy this is?