[FEATURE] Add json_array constructor function to PPL

[acarbonetto]

Is your feature request related to a problem?

As part of the RFC to add JSON functions, the json_array function would be useful to construct json objects with arrays.

• 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?

Tasks to complete:

• Add json_array(scalar_value) that returns an ARRAY object with scalars.
• Add json_array(field) that returns an ARRAY object with values from the field, where field can be a multi-value.
• Add json_array(json_object) that returns an ARRAY object with JSON_OBJECTs.
• Add json_array(json_array) that returns a mult-dimensional ARRAY object.
• Add json_array as part of the json_object construction; json_object(key, value [, key, value]*) -> json_object function, where value can also be a `json_array. see: [FEATURE] Add json_object constructor function to PPL #3208.

### `JSON_ARRAY`

**Description**

`json_array(<value>...)` Creates a JSON ARRAY flattening a list of multi-valued fields.

**Argument type:**
- A \<value\> can be any kind of value such as string, number, boolean, array, or json_object. 

**Return type:** ARRAY (Spark ArrayType)

An array of any supported data type for a valid JSON array.

Example:

    os> source=people | eval `json_array` = json_array(1, 2, 0, -1, 1.1, -0.11)
    fetched rows / total rows = 1/1

    +------------------------------+
    | json_array                   |
    +------------------------------+
    | [1.0,2.0,0.0,-1.0,1.1,-0.11] |
    +------------------------------+

    os> source=people | eval `json_array_object` = json_object("array", json_array(1, 2, 0, -1, 1.1, -0.11))

    fetched rows / total rows = 1/1
    +----------------------------------------+
    | json_array_object                      |
    +----------------------------------------+
    | {"array":[1.0,2.0,0.0,-1.0,1.1,-0.11]} |
    +----------------------------------------+

What alternatives have you considered?

N/A

Do you have any additional context?

opensearch-project/opensearch-spark#780 - PR to add feature to opensearch-spark PPL