elastic_ecs mapping: Consolidate x-ecs-source, x-ecs-destination, x-ecs-client, x-ecs-server objects

[Harmedox]

To start with, x-ecs-source, x-ecs-destination, x-ecs-client, x-ecs-server objects have the same attributes hence the need for consolidation. These attributes are also present in the x-oca-asset object (except for port).

The idea is to represent the IP and domain attributes in all 4 objects - to be consolidated - as ipv4-addr, ipv6-addr and domain SCO objects.