Add slack notification on failure for jobs triggered from gstg-gitlab-qa-orchestrated infra/deployer job

This will be used by the pipeline triggered from the gstg-gitlab-qa-orchestrated: infra/deployer job against a particular release deployed on staging.

Required for: https://ops.gitlab.net/gitlab-com/gl-infra/deployer/merge_requests/186

Related to https://gitlab.com/gitlab-org/quality/team-tasks/issues/235