API: add the config API as part of the v2 API.
API: add the config API as part of the v2 API.

After this patch, the API v2 will contain a config section with all the
configuration parametes.

get http://localhost:10000/v2

Will contain the config section.

An example for getting a configuration parameter:
curl http://localhost:10000/v2/config/listen_address

Signed-off-by: Amnon Heiman <ed5fc74c4692051ad0b19749fd7cea6ec2d74b9e@scylladb.com>

duarten/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla