### 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_
request.headers["x-amz-content-sha256"] = "UNSIGNED-PAYLOAD"
        presigned_client.meta.events.register(
            "before-sign.s3.Pu",
            handler=add_content_sha_header,
        )
        try:
            url = presigned_client.generate_presigned_url(
                "put_", Params={"Bucket": s3_bucket, "Key": key}
            )
            assert "x-amz-content-sha256" in url
            # some
            resp = .put(
                url,
                data="something",
                verify=False,
                headers={"x-amz-content-sha256": "UNSIGNED-PAYLOAD"},
            )
            assert resp.ok
            # if s
            resp = .put(url, data="something", verify=False)
            assert resp.status_code == 403
        finally:
            presigned_client.meta.events.unregister(
                "before-sign.s3.Pu",
                add_content_sha_header,
            )