[Purple] [.carto.geopkg] Groundwork for CARTO GeoPKG landing

[gfiorav]

Context

CARTO GeoPKG is a dataset format that we will introduce in CARTO as a collaboration with Bloomberg. This Issue keeps track of some prior work on optimising certain parts of the importer to ease with the new format's landing.

• [x] Use DataImport.user reflection instead of current_user https://github.com/CartoDB/cartodb/issues/12708
• [x] Metadata tools https://github.com/CartoDB/cartodb/issues/12821
• [ ] Decouple DataImport from TableRegistrar (new Carto::TableRegistrar)
• [ ] Decouple DataImport from Importer

[gfiorav]

Abandoned approach