Allow TCP backend to be configured
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=325084)
</details>
<!--IssueSummary end-->
Workhorse needs to be able to talk to gitlab-rails (Unicorn). Currently we have two ways of doing that:
- with TCP at `http://localhost:8080`
- with Unix sockets at a configurable socket path
What's missing here is connecting to gitlab-rails with TCP at an arbitrary address. We may want this for cloud-native deployments. cc @marin
issue