Put custom dns resolver behind feature flag

[dwelch-r7]

Resolves #18639 #18574 #18624

There is an issue with the custom dns resolver which is leading to some issues for users, I believe it was intended to be placed behind a feature flag dns_feature so that's what I'm doing here to resolve the issue and give us time to properly investigate the issue

[adfoster-r7]

Release Notes

Fixes a ipaddr.rb:622:in match: stack level too deep exception that was being raised on msfconsole startup

[adfoster-r7]

cc @sempervictus for visibility - I don't think you're using this functionality yet, but just in case 👍

[adfoster-r7]

We'll still need to fix the actual DNS issues with the new @@resolver pattern, but this should've been behind a feature flag from the get-go so this is all good for now 👍

[sempervictus]

All for!
Re DNS issues: apologies if i missed tags on other issues, happy to help tackle whatever stragglers/weirdness remains. Please dont be shy to email/slack me if im unresponsive here (the juggling of running chainsaws never ends, but getting stuff done here for the public is actually good for what passes for a "soul" in leathernecks 😉 ).