User Story:
As an OpenShift Engineer I want to enable job failure alert for 4.Y-e2e-external-vsphere-* to slack channel #forum-ocp-splat-alerts so we can make confidence of platform-external on OCP core for 4.Y.

Description:
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Alerts is not sent to the SPLAT alerts channel: https://redhat.enterprise.slack.com/archives/C064717U0D7 

Acceptance Criteria:
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Other Information:
https://docs.ci.openshift.org/docs/how-tos/notification/

issue created by splat-bot