feat: add respective `json_is` UDFs for JSON type

[CookiePieWw]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

#3686 #4515 #4230

What's changed and what's your intention?

As title. Add following json_is UDFs: json_is_null, json_is_array, json_is_object, json_is_int, json_is_float, json_is_string, json_is_bool. Also rename to_json to parse_json and add some sqlness tests.

Checklist

• [ ] I have written the necessary rustdoc comments.
• [ ] I have added the necessary unit tests and integration tests.
• [ ] This PR requires documentation updates.