Disable Workhorse preStop hook if health checker listener is enabled

What does this MR do?

We do not want to use a preStop hook with Workhorse when the health check listener is enabled because the health check listener needs to receive the SIGTERM immediately in order to set its readiness probe to "not ready". Workhorse has a gracefulShutdownDelay setting that should be used instead to drain existing connections.

This fixes the issue reported in gitlab-com/gl-infra/production#20745.

Changelog: fixed

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