Restrict use of global URL in certain packages

[lukekarrys]

This only lints for it in proxy-agent, pac-proxy-agent, and socks-proxy-agent since those were the packages changed in #242.

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Latest commit: c9c166c35e933b655bbb5a92e93b8bfb38472571

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Name	Status	Preview	Updated (UTC)
proxy-agents	✅ Ready (Inspect)	Visit Preview	Sep 8, 2023 7:24am

[TooTallNate]

Thank you!