If the proxy URL is in the form of `example.com` instead of a raw IP
address, and `example.com` isn't a well-known domain, then the default
URL resolution can fail.
The test setup:
A Linux machine runs a CoreDNS server with a custom entry: `10.254.7.38
example.com`. On a Windows machine, if the proxy URL is set to
`example.com`, the resolved address does **not** end up being
`10.254.7.38`.
Using `hickory_resolver` for more advanced DNS resolution fixes this
issue.
Release Notes:
- Fixed proxy URL resolution when using custom DNS entries.
bc68455320