Update: Return relevant follow-up URIs from all endpoints

[joeflack4]

Description

For most endpoints, we should be returning resolvable URLs instead of just values.

E.g., instead of models/ returning `["GDC", "PDC", ...], it would return URLs instead of or in addition to those lables, e.g.:

[
    {
        "label": "GDC",
        "uri": "https://terminology.ccdh.io/models/GDC/entities/"
    },
    ...
]