Modify checkRole.js and openapi specification to include UID in returned payload

According to Professor Wurst, moving forward, the demographic entries in the MongoDB backend will use the Keycloak UID hashes as keys (I am being loose with vocabulary here; I don't know what exactly all the terms are). The checkRole.js endpoint and the openapi.yaml specification file should probably be modified to include these hashes as another key-value pair in the returned payload, to avoid other repositories having to decode the tokens themselves and pull it out. I don't know at the time of writing (off the top of my head) which field in the JWT has the right value. I do know that it is automatically and already included in the generated JWTs, so this issue is as simple as figuring out which one is the correct UID that we want to use, and adding it to the returned json.