Implement obo_definition_citation, obo_xref, obo_synonym in OLS3 API

[ebispot]

Implement obo_definition_citation, obo_xref, obo_synonym in OLS3 API

[udp]

Outstanding problems: (1) Xref URLs are not implemented. OLS3 implementation:

(2) Synonym types are not implemented

[udp]

(1) To implement xref URLs we need to parse this 100 KB yaml file to map database name -> URL:

https://github.com/geneontology/go-site/blob/master/metadata/db-xrefs.yaml

(Are there any other files like this or is this the only one?)

There's no reason at present for this to be part of the dataload; we can download/parse it on boot in the backend (API server), store the map in memory, and use it to populate the fields in the OLS3 API. Then all you need to do to get an updated xrefs file is restart the backend and we don't need to add any noise to the databases.

It does mean our K8S backend deployment will require internet access, as we will be providing this as an URL rather than a file.

[udp]

(2) obo synonym type implementation from OLS3

will be very easy to implement, we just need an example to test against