Raft service levels are read-only in recovery mode. This patch adds check and proper error message when a user tries to modify service levels in recovery mode. Fixes https://github.com/scylladb/scylladb/issues/18827 Closes scylladb/scylladb#18841 * github.com:scylladb/scylladb: test/auth_cluster/test_raft_service_levels: try to create sl in recovery service/qos/raft_sl_dda: reject changes to service levels in recovery mode service/qos/raft_sl_dda: extract raft_sl_dda steps to common function