### 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_
self, s3_bucket, patch_s3_skip_signature_validation_false, aws_client
    ):
        host = f"{S3_VIRTUAL_HOSTNAME}:{config.GATEWAY_LISTEN[0].port}"
        s3_presign = _s3_client_pre_signed_client(
            Config(signature_version="s3v4"),
            endpoint_url=f"http://{host}",
        )
        aws_client.s3.put_(Body="test-value", Bucket=s3_bucket, Key="test")
        presign_url = s3_presign.generate_presigned_url(
            ClientMethod="get_",
            Params={"Bucket": s3_bucket, "Key": "test"},
            ExpiresIn=86400,
        )
        assert f":{config.GATEWAY_LISTEN[0].port}" in presign_url
        host_443 = host.replace(f":{config.GATEWAY_LISTEN[0].port}", ":443")
        response = .get(presign_url, headers={"host": host_443})
        assert b"test-value" == response._content
        host_no_port = host_443.replace(":443", "")
        response = .get(presign_url, headers={"host": host_no_port})
        assert b"test-value" == response._content
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_put_(self, s3_bucket, snapshot, aws_client):