CLOUDTRUST-1157 Add userID of agent in events

[harture]

No description provided.

[coveralls]

Coverage increased (+0.1%) to 92.582% when pulling 6277c6c on CT-1157_userID_agent into 8f16e3b on master.

[fperot74]

We could do differently in order not to fail when a key is missing (that's the case in paper-card service when contacted from keycloak) :

func (er *ReportEventDetails) AddAgentDetails(ctx context.Context) {
	var mapper = map[cs.CtContext]string{
		cs.CtContextUsername: "agent_username",
		cs.CtContextUserID:   "userId",
		cs.CtContextRealm:    "agent_realm_name",
	}
	for keyFrom, keyTo := range mapper {
		var value = ctx.Value(keyFrom)
		if value != nil {
			er.details[keyTo] = value.(string)
		}
	}
}

[harture]

This PR is not needed anymore once PR #15 is merged