consider using another sparql-client

[nvdk]

The current sparql-client package is effectively unmaintained, we should consider using a more modern package such as https://github.com/bergos/sparql-http-client

[nvdk]

actually, given the low level interface we provide it probably makes more sense to just use node-fetch/digest-fetch directly. See https://github.com/lblod/mu-auth-sudo/compare/feature/own-client-and-auth-support?expand=1 as an example