[FEATURE] Add PPL support to access values in array

[A-Gray-Cat]

Is your feature request related to a problem?
Currently, PPL doesn't support accessing values inside an array. For example,

{
    "items": ["a", "b", "c"]
}

Users can't select value a, b, or c using PPL.

What solution would you like?
Users can access the first element of the array by using syntax like eval first_item = items[0], or it can be retrieved directly using the fields command, e.g. fields items[0].

[YANG-DB]

@A-Gray-Cat thanks - we will review !