I want to add a field "slider" in /rest/V1/products/:sku

I created a custom module and in my di.xml i have added the following code

```
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd"> 
   <preference for="Magento\Catalog\Model\Product" type="mymod\Catalog\Model\Product" />
    <preference for="mymod\Catalog\Api\Data\ProductInterface" type="mymod\Catalog\Model\Product" />
    <preference for="mymod\Catalog\Api\ProductRepositoryInterface" type="Magento\Catalog\Api\ProductRepositoryInterface" />
    <preference for="mymod\Catalog\Api\Data\ProductInterface" type="Magento\Catalog\Api\Data\ProductInterface" />   
</config>

```

And I have added a method to Api/Data/ProductInterface

```
const slider = 'slider';

    public function getSlider();

    public function setSlider($slider);

```

I have implemented the two methods in 

```
<?php 

namespace mymod\Catalog\Model;

class Product extends \Magento\Catalog\Model\Product implements \Augmentes\Catalog\Api\Data\ProductInterface
{
    /**
     * {@inheritdoc}
     */
    public function getSlider()
    {
        return "test";
    }

    /**
     * Set slider value
     *
     * @param string $slider
     * @return $this
     */
    public function setSlider($slider)
    {
        return $this->setData('slider', "");
    } }

```

I also extended the ProductRepositoryInterface  

changed the routes in webapi.xml

Still the field not coming in response. Anyone please advise.

Thanks.