### 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.add_transformer(snapshot.transform.s3_api())
        for i in range(0, 1010, 1):
            body = "test-" + str(i)
            key = "test-key-" + str(i)
            aws_client.s3.put_(Bucket=s3_bucket, Key=key, Body=body)
        # tryi
        resp = aws_client.s3.get_(Bucket=s3_bucket, Key="test-key-1009")
        snapshot.match("get_-1009", resp)
        # tryi
        resp = aws_client.s3.get_(Bucket=s3_bucket, Key="test-key-0")
        snapshot.match("get_-0", resp)
        # acco
        # AWS 
        resp = aws_client.s3.list_s(Bucket=s3_bucket, MaxKeys=1010)
        assert 1010 >= len(resp["Contents"])
        resp = aws_client.s3.list_s(Bucket=s3_bucket, Delimiter="/")
        assert 1000 == len(resp["Contents"])
        # way 
        snapshot.add_transformer(
            snapshot.transform.jsonpath(
                "$..list-s.Contents", "<content>", reference_replacement=False
            )
        )
        snapshot.match("list-s", resp)
        next_marker = resp["NextMarker"]