Add conf setting for retrievers
Add conf setting for retrievers

They are used to configure our resource objects

latin-language-toolkit/arethusa,PonteIneptique/arethusa,fbaumgardt/arethusa,Masoumeh/arethusa,alpheios-project/arethusa,fbaumgardt/arethusa,Masoumeh/arethusa,alpheios-project/arethusa,alpheios-project/arethusa,fbaumgardt/arethusa,PonteIneptique/arethusa,latin-language-toolkit/arethusa