public void injectDocumentManangerForTests(DocumentTypeManager docTypeManager) {
        this.docTypeManager = docTypeManager;
    }
One client has one ClientFeederV3 shared between all client threads.
Contains logic for shutting down cleanly as the server is upgraded.

@author Haakon Dybdahl
vespaclient-container-plugin/src/main/java/com/yahoo/vespa/http/server/FeedHandlerV3.java