Added roles column definition for the KafkaNodePool CRD

[ppatierno]

Trivial PR to add the ROLES column definition to the KafkaNodePool CRD.
Using the string type from the possible ones from OpenAPI seems to be the way to print the list of roles.

NAME         DESIRED REPLICAS   ROLES
controller   3                  ["controller"]
kafka        3                  ["broker"]

and

NAME        DESIRED REPLICAS   ROLES
dual-role   3                  ["controller","broker"]

[fvaleri]

Useful. Thanks.