### 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_
Key="test-key",
            Body=content,
        )
        md = hashlib.md5(content.encode("utf-8")).digest()
        content_md5 = base64.b64encode(md).decode("utf-8")
        base_64_content_md5 = etag_to_base_64_content_md5(response["ETag"])
        assert content_md5 == base_64_content_md5
        hashes = ["__invalid__", "000", "not base64 encoded checksum", "MTIz"]
        for index, md5hash in enumerate(hashes):
            with pytest.raises(ClientError) as e:
                aws_client.s3.put_(
                    Bucket=s3_bucket,
                    Key="test-key",
                    Body=content,
                    ContentMD5=md5hash,
                )
            snapshot.match(f"md5-error-{index}", e.value.response)
        response = aws_client.s3.put_(
            Bucket=s3_bucket,
            Key="test-key",
            Body=content,
            ContentMD5=base_64_content_md5,
        )
        snapshot.match("success-put--md5", response)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_s3_upload_download_gzip(self, s3_bucket, snapshot, aws_client):