### 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_
resp_dict = xmltodict.parse(resp.content)
        assert "ListAllMyBucketsResult" in resp_dict
        # vali
        # to p
        assert (
            resp_dict["ListAllMyBucketsResult"].pop("@xmlns")
            == "http://s3.amazonaws.com/doc/2006-03-01/"
        )
        list_buckets_tags = list(resp_dict["ListAllMyBucketsResult"].keys())
        assert list_buckets_tags[0] == "Owner"
        assert list_buckets_tags[1] == "Buckets"
        # List
        bucket_url = _bucket_url(s3_bucket)
        resp = s3_http_client.get(bucket_url, headers=headers)
        assert b'<?xml version="1.0" encoding="UTF-8"?>\n' in get_xml_content(resp.content)
        resp_dict = xmltodict.parse(resp.content)
        assert "ListBucketResult" in resp_dict
        assert resp_dict["ListBucketResult"]["@xmlns"] == "http://s3.amazonaws.com/doc/2006-03-01/"
        # vali
        # Buck
        list_s_tags = list(resp_dict["ListBucketResult"].keys())
        assert list_s_tags.index("Name") < list_s_tags.index("Contents")
        assert list_s_tags[-1] == "Contents"
        # List
        list_s_v2_url = f"{bucket_url}?list-type=2"
        resp = s3_http_client.get(list_s_v2_url, headers=headers)
        assert b'<?xml version="1.0" encoding="UTF-8"?>\n' in get_xml_content(resp.content)
        resp_dict = xmltodict.parse(resp.content)
        assert "ListBucketResult" in resp_dict
        assert resp_dict["ListBucketResult"]["@xmlns"] == "http://s3.amazonaws.com/doc/2006-03-01/"