### 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_
"Id": "test-inventory",
            "Destination": {
                "S3BucketDestination": {
                    "Bucket": f"arn:aws:s3:::{dest_bucket}",
                    "Format": "CSV",
                }
            },
            "IsEnabled": True,
            "IncludedVersions": "All",
            "OptionalFields": ["Size", "ETag"],
            "Schedule": {"Frequency": "Daily"},
        }
        put_inv_config = aws_client.s3.put_bucket_inventory_configuration(
            Bucket=src_bucket,
            Id=inventory_config["Id"],
            InventoryConfiguration=inventory_config,
        )
        snapshot.match("put-inventory-config", put_inv_config)
        list_inv_configs = aws_client.s3.list_bucket_inventory_configurations(Bucket=src_bucket)
        snapshot.match("list-inventory-config", list_inv_configs)
        get_inv_config = aws_client.s3.get_bucket_inventory_configuration(
            Bucket=src_bucket,
            Id=inventory_config["Id"],
        )
        snapshot.match("get-inventory-config", get_inv_config)
        del_inv_config = aws_client.s3.delete_bucket_inventory_configuration(
            Bucket=src_bucket,
            Id=inventory_config["Id"],
        )
        snapshot.match("del-inventory-config", del_inv_config)