firewall endpoint(slices) should be created by fcm instead of firewall-controller

[mwennrich]

Description

Currently, the firewall-controller creates the endpoints for the nftables-exporter and node-exporter in the firewall namespace.

In clusters with two or more firewalls, they constantly overwrite each other's endpoints.

The endpoint(slice) should instead be managed by the FCM and should contain the addresses of all firewalls in the cluster.