[Feature Request]: UseUnixDomainSocket() with HostApplicationBuilder

**Is your feature request related to a problem? Please describe.**
Per @davidfowl, [we have moved away from the ceremony](https://github.com/dotnet/runtime/discussions/81090#discussioncomment-4784551) of the generic host.

However, the `HostApplicationBuilder` returned from `Host.CreateApplicationBuilder()` does not have the extension classes in CoreWCF to use `UseUnixDomainSocket()`. It expects an `IHostBuilder`, which `HostApplicationBuilder` does not implement.

**Describe the solution you'd like**
I'd like to be able to call `UseUnixDomainSocket()` on a `HostApplicationBuilder`.

**Describe alternatives you've considered**
I was first going to locally add an extension class, but it won't work because of the protection level (`internal`) of `UnixDomainSocketHostedService`.

I was going to send a PR with a new extension class, but I can't reference `IHostApplicationBuilder` because it only targets `net6.0` with `6.0` NuGets. I'd have to either multi-target the solution or upgrade the NuGets without upgrading the TFM, which I don't think would even work and wouldn't be approved.

I basically need the solution to be upgraded to `net8.0` or multi-targeted before I can do anything. I doubt you want an outside PR to upgrade everything to `net8.0` and I don't know what the plan is there. It's been LTS for a long time, so I assume it wasn't done for a reason.

**Additional context**
I'm trying to avoid the extra stuff registered and the ceremony of `Host.CreateDefaultBuilder()`