conf: update commented out experimental_features

update commented out experimental_features to reflect the latest
experimental features:

- in 4f23eec4, "raft" was renamed to "consistent-topology-changes".
- in 2dedb5ea, "alternator-ttl" was moved out of experimental features.
- in 5b1421cc, "broadcast-tables" was added to experimental features.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#15407

conf/scylla.yaml

@@ -278,8 +278,9 @@ batch_size_fail_threshold_in_kb: 1024
 # experimental_features:
 #     - udf
 #     - alternator-streams
-#     - alternator-ttl
-#     - raft
+#     - consistent-topology-changes
+#     - broadcast-tables
+#     - keyspace-storage-options
 #     - tablets
 
 # The directory where hints files are stored if hinted handoff is enabled.