fix nested behave for JsonRepeatable

[KotenkoSerge]

Found that JsonRepeatable behave incorect when it has nested structure. Let's take a look at request example:

"json_repeatable": 
    [
        {
            "title": "Title 1",
            "badge": "badge 1",
            "nested_json_repeatable": [
                {
                    "uuid": "891e1a21-c655-40c2-9026-7e2c7b52b285",
                    "title": "nested 1 title 1",
                    "url": "http://localhost/1_1",
                    "description": "Description 1"
                },
                {
                    "uuid": "ef20be68-7510-4455-9a39-67185005fe34",
                    "title": "nested 1 title 2",
                    "url": "http://localhost/1_2",
                    "description": "Description 2"
                }
            ]
        },
        {
            "title": "Title 2",
            "nested_json_repeatable": [
                {
                    "uuid": "9c324bee-c55d-40e5-a7a0-55b2ac6ac752",
                    "title": "nested 2 title 2",
                    "url": "http://localhost/2_2",
                    "description": "Description 2"
                }
            ]
        }
    ]

So what did I found is that JsonRepeatable does not fill values field by field when JsonRepeatable is inside other JsonRepeatable, it directly takes whole array from request by key (nested_json_repeatable from my example) and put it to model's value without any validation as validation rules also broken when JsonRepeatable is nested.
This merge request adds, I would call it, "pseudo" recursion for nested JsonRepeatable and nested rules