[FEATURE] Add json_extract function to PPL

[acarbonetto]

Is your feature request related to a problem?

As part of the RFC to add JSON functions, the json_extract function would be useful to extract specific objects and scalars from an existing json_object.

• META RFC: [META]Add PPL JSON extended functions support #3027
• PPL RFC: [RFC] Add PPL JSON extended functions support #3028
• Related Spark PPL PR: Support PPL JSON functions: construction and extraction opensearch-spark#780

What solution would you like?

### `JSON_EXTRACT`

**Description**

`json_extract(doc, path [, path]...)` Extracts a json value or scalar from a json document based on the path(s) specified.

**Argument type:** STRING, STRING

**Return type:** STRING | NULL | JSON ARRAY

- Returns a JSON array for multiple paths or if the path leads to an array.  
- Return null if path is not valid.

Example:

    os> source=people | eval `json_extract(json('{"a":"b"}'), '$.a')` = json_extract('{"a":"b"}', '$a')
    fetched rows / total rows = 1/1
    +----------------------------------+
    | json_extract('{"a":"b"}', 'a')   |
    +----------------------------------+
    | b                                |
    +----------------------------------+

    os> source=people | eval `json_extract(json('{"a":[{"b":1},{"b":2}]}'), '$.a[1].b')` = json_extract('{"a":[{"b":1},{"b":2}]}', '$.a[1].b')
    fetched rows / total rows = 1/1
    +-----------------------------------------------------------+
    | json_extract('{"a":[{"b":1.0},{"b":2.0}]}', '$.a[1].b')   |
    +-----------------------------------------------------------+
    | 2.0                                                       |
    +-----------------------------------------------------------+

    os> source=people | eval `json_extract('{"a":[{"b":1},{"b":2}]}', '$.a[*].b')` = json_extract(json('{"a":[{"b":1},{"b":2}]}'), '$.a[*].b')
    fetched rows / total rows = 1/1
    +-----------------------------------------------------------+
    | json_extract('{"a":[{"b":1.0},{"b":2.0}]}', '$.a[*].b')   |
    +-----------------------------------------------------------+
    | [1.0,2.0]                                                 |
    +-----------------------------------------------------------+

    os> source=people | eval `invalid_json` = json_extract(json('{"invalid": "json"'))
    fetched rows / total rows = 1/1
    +----------------+
    | invalid_json   |
    +----------------+
    | null           |
    +----------------+

What alternatives have you considered?

N/A

Do you have any additional context?

Related spark PPL PR: opensearch-project/opensearch-spark#780

[kenrickyap]

Hi @YANG-DB @LantaoJin currently working on this ticket and was wondering if I could import the following library: https://github.com/json-path/JsonPath. It has APACHE 2.0 licence and would be ideal in handling the path traversal that needs to be done.

This would be more robust than implementing the functionality ourselves and would be useful to other json functions.

[YANG-DB]

@kenrickyap I agree