### 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_
snapshot.match("head_", head_)
        _attrs = aws_client.s3.get__attributes(
            Bucket=s3_bucket,
            Key=_key,
            Attributes=["StorageClass"],
        )
        snapshot.match("-attrs", _attrs)
        with pytest.raises(ClientError) as e:
            aws_client.s3.copy_(
                Bucket=s3_bucket, CopySource=f"{s3_bucket}/{_key}", Key=_key
            )
        snapshot.match("copy--in-place-no-change", e.value.response)
        # it 
        # an
        # co
        resp = aws_client.s3.copy_(
            Bucket=s3_bucket,
            CopySource=f"{s3_bucket}/{_key}",
            Key=_key,
            ChecksumAlgorithm="SHA256",
            StorageClass=StorageClass.STANDARD,
        )
        snapshot.match("copy--in-place-with-storage-class", resp)
        _attrs = aws_client.s3.get__attributes(
            Bucket=s3_bucket,
            Key=_key,
            Attributes=["StorageClass"],
        )
        snapshot.match("-attrs-after-copy", _attrs)
        # ge