Add Kubernetes discovery support in Network Connector

Currently, the Network Connector supports several discovery agents (multicast, ...).

To integrate smoothly in a Kubernetes environment, we could provide a Kubernetes discovery agent able to discover brokers on the kube (exactly as we did on Karaf Cellar).

NB: we could also consider other discovery agents (hazelcast, ignite, ...), we can create specific issue for that.

Start by examining the Network Connector’s existing discovery agents and the Karaf Cellar integration referenced in the issue. Define how a Kubernetes discovery agent should discover brokers, then identify suitable implementation and test entry points; the issue does not name specific files or tests.

Written by the indexing model from the issue text.