add examples about migrating from nginx ingress controller

### Issue description

Due to most people started to get in touch with Kubernetes ingress is using `nginx ingress controller`, so it is likely to use a lot of nginx ingress's annotations. It's a good idea to add some example about migrating from nginx ingress controller. Such as

```
nginx.ingress.kubernetes.io/configuration-snippet: |
rewrite ^/api/(.*) /$1 break;
```

```
nginx.ingress.kubernetes.io/proxy-body-size
```

and so on.

No documentation file or test is named in the issue. Start by locating the existing migration examples and reviewing the requested nginx ingress annotations, including configuration-snippet and proxy-body-size. Done means adding clear migration examples for the supported annotations and verifying the documentation renders correctly.

Written by the indexing model from the issue text.