Replace usage of old node:url api with WHATWG one in pushgateway.js

[yvon-morice-wmx]

Related to #743

Replaces usage of url.urlParse and url.resolve from node:url by new url.Url from same package as these functions have been deprecated and trigger a warning on usage.

Changes based on code and documentation available at https://nodejs.org/api/url.html#urlresolvefrom-to and https://github.com/nodejs/userland-migrations/tree/main/recipes/node-url-to-whatwg-url

[jdmarshall]

If you're going to go through the trouble of unwinding URL->url attribute copying it'd be better off to work with URL internally and just do the jiggery pokery for forwarding the old style requestOptions over the top, so we don't round-trip to the legacyUrlResolve function twice.

[jdmarshall]

Still hasn't removed the old url, just uses it less.

Until the http request is being made with URL I don't believe this PR achieves the goal of replacing the legacy url parser.

Also this PR will need pinning tests.

So what I'd want to see is:

• no urls, full stop
• No manual interpolation. I'm a stickler about this an every time I haven't been has turned into a security hole. And you shouldn't need it at any rate if we stop going back and forth between.
• splitting the URL and the request Options before calling http.request(url, options) removes the old format and any translation issues lurking there, and also solves the no interpolation problem handily.

This is a Kernighan's Law situation. It's a "there are no obvious bugs" vs "there are obviously no bugs" (Hoare) scenario. The new version should be obviously correct or we haven't really fixed the hole, just punched new ones.