### 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_
Bucket=s3_bucket,
            CopySource=src__path,
            Key=key,
            MetadataDirective="REPLACE",
        )
        snapshot.match("copy--in-place", response)
        copy_etag = response["CopyResult"]["ETag"]
        # etag
        assert copy_etag != multipart_etag
    @markers.aws.validated
    @pytest.mark.skipif(
        condition=LEGACY_V2_S3_PROVIDER,
        reason="Behaviour is not in line with AWS, does not validate properly",
    )
    def test_get__part(self, s3_bucket, s3_multipart_upload, snapshot, aws_client):
        snapshot.add_transformer(
            [
                snapshot.transform.key_value("Location"),
                snapshot.transform.key_value("Bucket"),
            ]
        )
        key = "test.file"
        content = "test content 123"
        response = s3_multipart_upload(bucket=s3_bucket, key=key, data=content, parts=2)
        snapshot.match("multipart-upload", response)
        head__part = aws_client.s3.head_(Bucket=s3_bucket, Key=key, PartNumber=2)
        snapshot.match("head--part", head__part)
        get__part = aws_client.s3.get_(Bucket=s3_bucket, Key=key, PartNumber=2)
        snapshot.match("get--part", get__part)
        with pytest.raises(ClientError) as e: