Implement for `json` in `isRefPointerToSchema()`

[SOHELAHMED7]

File: src/lib/openapi/PropertySchema.php

public function isRefPointerToSchema():bool
    {
        return $this->refPointer &&
            ((strpos($this->refPointer, self::REFERENCE_PATH) === 0) ||
                (str_ends_with($this->uri, '.yml')) || (str_ends_with($this->uri, '.yaml'))); <----- TODO this can be `json` also
    }