### 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_
assert datetime.datetime.strptime(last_modified, RFC1123)
        assert last_modified.endswith(" GMT")
        get_obj_resp = s3_http_client.get(
            _url, headers={"x-amz-content-sha256": "UNSIGNED-PAYLOAD"}
        )
        last_modified: str = get_obj_resp.headers["Last-Modified"]
        assert datetime.datetime.strptime(last_modified, RFC1123)
        assert last_modified.endswith(" GMT")
        _attrs_url = f"{_url}?attributes"
        get_obj_attrs_resp = s3_http_client.get(
            _attrs_url,
            headers={"x-amz-content-sha256": "UNSIGNED-PAYLOAD", "x-amz--attributes": "ETag"},
        )
        last_modified: str = get_obj_attrs_resp.headers["Last-Modified"]
        assert datetime.datetime.strptime(last_modified, RFC1123)
        assert last_modified.endswith(" GMT")
        copy__url = f"{bucket_url}/copied-key"
        copy_resp = s3_http_client.put(
            copy__url,
            headers={
                "x-amz-content-sha256": "UNSIGNED-PAYLOAD",
                "x-amz-copy-source": f"{bucket_url}/{_key}",
            },
        )
        copy_resp_dict = xmltodict.parse(copy_resp.content)
        copy_timestamp: str = copy_resp_dict["CopyResult"]["LastModified"]
        assert_timestamp_is_iso8061_s3_format(copy_timestamp)
    # This test doesn't work against AWS anymore because of some authorization error.
    @markers.aws.only_localstack
    def test_s3_delete_s_trailing_slash(self, aws_http_client_factory, s3_bucket, aws_client):