All `http` commands now support connecting via Unix domain sockets using
the `--unix-socket` flag, enabling communication with local services
like Docker daemon, systemd, and other IPC services.

# Usage

```nu
# Query Docker daemon via Unix socket
http get --unix-socket /var/run/docker.sock http://localhost/containers/json

# POST to a local service
http post --unix-socket ./my-service.sock http://api/endpoint {data: "value"}
```

The URL's hostname is used for the HTTP `Host` header while the
connection goes through the specified socket path.

# Platform support

Unix systems (Linux, macOS, BSD) and Windows!

# Testing

Manually tested, on POSIX only, with a real-world use case:
[xs.nu](https://gist.github.com/cablehead/b853c7f6bea96fab49a66c0352f10574#file-xs-nu-L24-L61)
- a Nushell wrapper for [cross.stream](https://github.com/cablehead/xs)
that uses the new Unix socket support.

# Notes

The `--unix-socket` flag follows curl's design, where it accepts a path
to connect through the Unix domain socket instead of using TCP.

# Documentation

See nushell/nushell.github.io#2059