feat(ext/fetch): Allow specifying a custom DNS resolver for fetch calls

[SkaillZ]

Implements #17165

• Adds a new field to deno_fetch::Options to allow specifying a custom DNS resolver
• Bumps reqwest to the latest version to use this feature

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[aapoalas]

Hello and thank you for the contribution.

Before this can be merged, it will at least need a test showing how this can be used from Deno, and of course testing that it works. Currently I can only see Rust side implementations for supporting this feature but not how it can be used.

A further issue is of course that if this is adding custom Deno options to the Fetch API's options bag (eg. fetch(url, { dnsResolver }) then that may require some WinterCG-level discussions.

[SkaillZ]

@aapoalas I think there's a misunderstanding here, I didn't mean to expose an option to customize the DNS resolver via JavaScript. It's meant to instead give custom runtimes more control over DNS resolution on the Rust side (similarly to how FetchPermissions is used).

Regarding tests, I couldn't find any in fetch.rs, so I'm not sure where the best place for tests concerning ext/fetch would be. I'd be happy to write some tests if you could point me to the right place to add them to.