"odo service list" should output Operator backed service as "<servicekind>/<servicename>"

[dharmit]

/kind feature
/kind discussion
/area UX

Currently, we're listing services backed by Operators as below:

$ odo service list
NAME        TYPE            AGE
example     Cockroachdb     3s
example     EtcdCluster     3m22s

As proposed in #3557, if a user wants to connect to EtcdCluster named example, they need to do odo link EtcdCluster/example. For better UX, it would be helpful if we list the services as below instead:

$ odo service list
NAME                          AGE
Cockroachdb/example           3s
EtcdCluster/example           3m22s
EtcdCluster/myawesomeetcd     3s

Originally posted by @dharmit in #2920 (comment)

[dharmit]

I have opened a PR based on the discussion had in #2920. Completely open to suggestions/discussion if we would like to have different output format.