### 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_
<Delete xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
              <>
                <Key>{_key_1}</Key>
              </>
              <>
                <Key>{_key_2}</Key>
              </>
            </Delete>
            """
        md = hashlib.md5(data.encode("utf-8")).digest()
        contents_md5 = base64.b64encode(md).decode("utf-8")
        header = {"content-md5": contents_md5, "x-amz-request-payer": "requester"}
        r = .post(url=url, data=data, headers=header)
        assert 200 == r.status_code
        response = xmltodict.parse(r.content)
        snapshot.match("multi-delete-with-", response)
        response = aws_client.s3.list_s(Bucket=s3_bucket)
        snapshot.match("list-remaining-s", response)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        paths=[
            "$..Prefix",
        ]
    )
    def test_s3_batch_delete_s(self, s3_bucket, snapshot, aws_client):
        snapshot.add_transformer(snapshot.transform.s3_api())
        snapshot.add_transformer(snapshot.transform.key_value("Key"))
        delete_ = []
        for _ in range(5):
            key_name = f"key-batch-delete-{short_uid()}"