Implement user-management API

auth/auth.go

cmd/rednerd/admin_password.go

models/db_helpers.go

models/user_db.go

models/userinfo.go

restapi/configure_rednerd.go

restapi/embedded_spec.go

restapi/handlers/auth-userinfo.go

restapi/handlers/errors.go

restapi/handlers/user-add.go

restapi/handlers/user-delete.go

restapi/handlers/user-get.go

restapi/handlers/user-list.go

restapi/handlers/user-update.go

restapi/operations/logging.go

restapi/operations/prometheus.go

restapi/operations/rednerd_api.go

restapi/operations/user_management/user_add_parameters.go

restapi/operations/user_management/user_delete.go

restapi/operations/user_management/user_delete_parameters.go