Feature request: ST_Buffer support

[aricooperdavis]

It would be brilliant if the API spatial scopes could be expanded to support ST_Buffer, e.g.

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whereBuffer

Filters records within a buffer. Uses ST_Buffer.

parameter name	type
$column	Geometry \ string
$geometryOrColumn	Geometry \ string
$value	int \ float

Example

```php Place::create(['location' => new Point(1, 1.5)]); $placesCountWithinBuffer = Place::query() ->whereBuffer('location', Polygon::fromJson('{"type":"Polygon","coordinates":[[[-1,-1],[1,-1],[1,1],[-1,1],[-1,-1]]]}'), 3) ->count(); echo $placesCountWithinBuffer; // 1 ```

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I will see if I can submit a PR, but with Christmas coming up it won't be for a little while!

[MatanYadaev]

I'll be happy to accept a PR. Thanks!