Nested JSON support

[WeihanLi]

Is your feature request related to a problem? Please describe.

It would help us use complex json more easily

http pie.dev/post \
  platform[name]=HTTPie \
  platform[about][mission]='Make APIs simple and intuitive' \
  platform[about][homepage]=httpie.io \
  platform[about][homepage]=httpie.io \
  platform[about][stars]:=54000 \
  platform[apps][]=Terminal \
  platform[apps][]=Desktop \
  platform[apps][]=Web \
  platform[apps][]=Mobile

{
    "platform": {
        "name": "HTTPie",
        "about": {
            "mission": "Make APIs simple and intuitive",
            "homepage": "httpie.io",
            "stars": 54000
        },
        "apps": [
            "Terminal",
            "Desktop",
            "Web",
            "Mobile"
        ]
    }
}

Additional context

https://httpie.io/docs/cli/nested-json