### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- following the [installation steps](https://docs.localstack.cloud/getting-started/installation/) fails when validating localstack configuration

- error
![image](https://github.com/localstack/localstack/assets/10324554/d82ef62e-c8b8-402e-8195-e691733cfeb1)

- localstack is indeed running
![image](https://github.com/localstack/localstack/assets/10324554/44d7180a-5090-416d-afa9-c4eaaedca33e)


### Expected Behavior

- localstack can consume the path I pass `--file`

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker compose up -d
    localstack config validate --file ./compose.yaml


### Environment

```markdown
OS: Ubuntu 20.04
    LocalStack: latest
```


### Anything else?

- you can reproduce [on this branch](https://github.com/noahehall/localstack/tree/rds) if it still exists
  - else switch to the develop branch
image_name = os.environ.get("IMAGE_NAME")
    if not image_name:
        image_name = constants.DOCKER_IMAGE_NAME
        if is_api_key_configured():
            image_name = constants.DOCKER_IMAGE_NAME_PRO
    return image_name
def extract_port_flags(user_flags, port_mappings: PortMappings):
    regex = r"-p\s+([0-9]+)(\-([0-9]+))?:([0-9]+)(\-([0-9]+))?"
    matches = re.match(".*%s" % regex, user_flags)
    if matches:
        for match in re.findall(regex, user_flags):
            start = int(match[0])
            end = int(match[2] or match[0])
            start_target = int(match[3] or start)
            end_target = int(match[5] or end)
            port_mappings.add([start, end], [start_target, end_target])
        user_flags = re.sub(regex, r"", user_flags)
    return user_flags
class LocalstackContainer: