print_json: support ensure_ascii parameter

[senpos]

Hey!

Recently I needed to print a JSON file which had many non-ascii symbols.

I noticed that rich added an utility function and a CLI tool to print JSON beautifully with colors, but turns out the default json.dump settings make this file

[{"city": "Lübeck", "state": "Schleswig-Holstein", "status": "🟢"}, {"city": "Freiburg im Breisgau", "state": " Baden-Württemberg", "status": "🔴"}]

to look like this:

[
  {
    "city": "L\u00fcbeck",
    "state": "Schleswig-Holstein",
    "status": "\ud83d\udfe2"
  },
  {
    "city": "Freiburg im Breisgau",
    "state": " Baden-W\u00fcrttemberg",
    "status": "\ud83d\udd34"
  }
]

Notice that characters like ü and emojis were escaped, which does not look good. ;)

While it is a safe default, I would love to have an option to change this behavior.
It should be as easy as allowing to set the ensure_ascii parameter.

Would you consider merging a PR that adds this functionality?