Advertise features supported by this node, so that other nodes can know
this info. For example, on a 3 node cluster with supported_features ==
FEATURE1 and FEATURE2, it looks like:
cqlsh> SELECT supported_features from system.peers;
supported_features
--------------------
FEATURE1,FEATURE2
FEATURE1,FEATURE2
(2 rows)
cqlsh> SELECT supported_features from system.local;
supported_features
--------------------
FEATURE1,FEATURE2
(1 rows)