### 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_
response = aws_client.s3.list_s(Bucket=s3_bucket)
        assert response["ResponseMetadata"]["HTTPStatusCode"] == 200
        assert len(response["Contents"]) == 1
        snapshot.match("list-remaining-s", response)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        paths=["$..DeleteResult.Deleted..VersionId", "$..Prefix", "$..DeleteResult.@xmlns"]
    )
    def test_s3_batch_delete_public_s_using_(
        self, s3_bucket, allow_bucket_acl, snapshot, aws_client, anonymous_client
    ):
        # only 
        # http
        snapshot.add_transformer(snapshot.transform.s3_api())
        _key_1 = "key-created-by-anonymous-1"
        _key_2 = "key-created-by-anonymous-2"
        aws_client.s3.put_bucket_acl(Bucket=s3_bucket, ACL="public-read-write")
        anon = anonymous_client("s3")
        anon.put_(
            Bucket=s3_bucket, Key=_key_1, Body="This body document", ACL="public-read-write"
        )
        anon.put_(
            Bucket=s3_bucket,
            Key=_key_2,
            Body="This body document #2",
            ACL="public-read-write",
        )
        # TODO 
        url = f"{_bucket_url(s3_bucket, localstack_host=get_localstack_host().host)}?delete"
        data = f"""