### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- Localstack fails with HTTP 500, error code "InternalError", message "not enough values to unpack (expected 2, got 1)" when `CopySource` is an invalid string for `copy_object` API.

### Expected Behavior

- For the same API `copy_object`, the cloud fails with HTTP 400, error code "InvalidArgument".
- Localstack should handle invalid `CopySource` i.e., it is a dictionary with one value or an invalid string not adhering to "{bucket}/{key}" format.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

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

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    botoclient.copy_object(CopySource="Invalid_random_string", Bucket="test_bucket", Key=key) 


 test_bucket is a valid bucket.  

### Environment

```markdown
- OS: Ubuntu 22.04.2 LTS
- LocalStack: 2.1.0
- boto3: 1.28.6
```


### Anything else?

_No response_
# put 
        response = .put(url, data="content 123")
        # if w
        if not verify_signature and not is_aws_cloud():
            assert response.ok, f"response returned {response.status_code}: {response.text}"
            # resp
            assert not response.text
        else:
            assert response.status_code == 403
            exception = xmltodict.parse(response.content)
            snapshot.match("no-meta-headers", exception)
        # put 
        response = .put(url, data="content 123", headers={"x-amz-meta-foo": "bar"})
        # asse
        assert response.ok
        response = aws_client.s3.head_(Bucket=s3_bucket, Key=_key)
        assert response["Metadata"]["foo"] == "bar"
        snapshot.match("head_", response)
        # asse
        response = .put(url, data="content 123", headers={"x-amz-meta-wrong": "wrong"})
        # if w
        if not verify_signature and not is_aws_cloud():
            assert response.ok, f"response returned {response.status_code}: {response.text}"
        else:
            assert response.status_code == 403
            exception = xmltodict.parse(response.content)
            snapshot.match("wrong-meta-headers", exception)
        head_ = aws_client.s3.head_(Bucket=s3_bucket, Key=_key)
        if not verify_signature and not is_aws_cloud():
            assert head_["Metadata"]["wrong"] == "wrong"