Connecting with reference databases

Context: During processing, we already associate entries with "our" springerdb and aflow prototypes. There will be more sources in the future. This is always a licence sensitive issue.

We might want to add more "reference databases" in the future. The references should be more prominently displayed in the GUI. We should create a more general system to "include"/connect other databases (without necessarely importing their data).

The optimade API is good at searching, at least based on elements, formulas. The results would also contain positions, lattice. Optimade is provided by increasing number of databases (aflow, oqmd, mp, cod, ...). Some of the providers might also give symmetries, etc.

We need

• common metadata schema for references
• abstract python interface for looking up a structure "on the internet"
• example implementation of that interface for optimade (and all its providers), springer, aflow-prototypes
• api (and cache) on top of this interface
• a card on the entry overview page that uses this API to "search" for related data "on-the-fly"
• potentially turning this on-demand-query system into an index-databases-and-label-during-processing system
• related: we might do a similar thing (at-least have a similar UI) to represented related calculations within NOMAD.