Use FQDN for endpoint hosts to work with HTTP proxies

### Describe the problem.

This has been a regular issue on Polaris and now Frontier. The use of raw IPs in the endpoint configs means that clients get proxied, presumably because the HTTP proxy only skips certain domains.

### How did you install ProxyStore?

```console
N/A
```

### ProxyStore Version

N/A

### Python Version

N/A

### OS and Platform

N/A