[Security solution] Add user.target.name in Authentications table

[naj-h]

In Explore > Hosts > Authentications, the table does not contain the user.target.name field.

Sometimes the user.name field contains the computer account which ends with a $. This username is normally hostname$. When this happens the security analysts need to look at the user.target.name field to see which user account is being used. As this happens often on a windows domain, it would help if the siem pages displayed the user.target.name field alongside the user.name field.

This field is mapped to user.target.name in ECS. elastic.co/guide/en/ecs/current/ecs-user.html

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/security-threat-hunting (Team:Threat Hunting)