Add support for COPY with --exclude

https://docs.docker.com/reference/dockerfile/#copy

<img width="792" alt="Screenshot 2024-05-23 at 19 09 11" src="https://github.com/hadolint/language-docker/assets/3893573/fbc403ae-82fb-48bb-85c5-de03ff82fbf2">

Example dockerfile: 

```
FROM scratch
COPY --exclude=README.md . /app
```

Example error: 

```
dockerfiles/Dockerfile:2:6 invalid flag: --exclude
```