[WIP] Install nginx with ngx_small_light

Install nginx with [cubicdaiya/ngx_small_light](https://github.com/cubicdaiya/ngx_small_light) on Docker container.

If you want to download WebP image, just access below.

```
http://localhost:8000/small_light(dw=200,dh=200,of=webp)/img/image.jpg
```

## TODO
- [x] Specify server name
 - from environment variable (d7d1f5d)
- [x] Specify S3 host
 - from environment variable (d7d1f5d)
- [ ] Connect with web container