### 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())
        key = "my-key"
        # ht
        tranfer_config = TransferConfig(multipart_threshold=5 * KB, multipart_chunksize=1 * KB)
        file = tmpdir / "test-file.bin"
        data = b"1" * (6 * KB)  # cr
        file.write(data=data, mode="w")
        aws_client.s3.upload_file(
            Bucket=s3_bucket, Key=key, Filename=str(file.realpath()), Config=tranfer_config
        )
        obj = aws_client.s3.get_(Bucket=s3_bucket, Key=key)
        assert obj["Body"].read() == data, f"body did not contain expected data {obj}"
        snapshot.match("get_", obj)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],