Workhorse: allow disabling non-TLS listener
With !81400, we've introduced TLS support for Workhorse, and in https://gitlab.com/gitlab-org/gitlab/blob/c6649670770bf6c5b6f97de6d4a4ffdf91991241/workhorse/main.go#L247 we're always creating a listener from the `-listenAddr -listenNetwork` flags passed to Workhorse (defaulting to `localhost:8181`, `tcp` respectively) which means we'll always have a `localhost:8181` TCP listener even if not passed. We should make it possible to disable the non-TLS listener if desired (and maybe still keep the default listener to :8181 or verify that this doesn't break liveness/readiness checks if it's changed)
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