dns: support for custom hosts

[FabianPonce]

This PR adds support for passing host resolver information to Lima, allowing the internal DNS resolver to resolve any custom names you wish. This is particularly useful for services that do not use getaddrinfo, ie. specific nginx, envoy configurations.

[abiosoft]

Hi, thanks for this.

Rather than bringing the entire hostResolver config into Colima, I would recommend supporting config for only the custom hosts.

It can easily be an array flag e.g. --custom-host=host.docker.internal=host.lima.internal
And a config section for customHosts that is a map[string]string.

We would also need to keep host.docker.internal as default/base value and only append the user specified values.

[FabianPonce]

I agree, I think that would be a much cleaner solution in general. I'll make some changes and re-request review.

[FabianPonce]

@abiosoft I felt that the custom hosts functionality, being related to DNS, should live somewhere near the resolver settings, so I moved this under the network section. I'm happy to break it out into the originally suggested location if you still think that's more suitable.

I also renamed the DNS Resolvers list in the config struct to DNSResolvers to make that more clear in the code. I left the naming in the yaml alone as network.dns, though, to keep backwards compatibility for people using that.