### 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_
# put 
        url = presigned_client.generate_presigned_url(
            "put_",
            Params={"Bucket": s3_bucket, "Key": _key, "Metadata": metadata},
        )
        assert "x-amz-meta-foo=bar" in url
        response = .put(url, data="content 123", verify=False)
        assert response.ok, f"response returned {response.status_code}: {response.text}"
        # resp
        assert not response.text
        # asse
        response = aws_client.s3.head_(Bucket=s3_bucket, Key=_key)
        assert response.get("Metadata", {}).get("foo") == "bar"
        snapshot.match("head_", response)
        # asse
        response = .put(url, data="content 123", headers={"x-amz-meta-wrong": "wrong"})
        # if w
        if not verify_signature and not is_aws_cloud():
            assert response.ok, f"response returned {response.status_code}: {response.text}"
        else:
            assert response.status_code == 403
            exception = xmltodict.parse(response.content)
            snapshot.match("wrong-meta-headers", exception)
        head_ = aws_client.s3.head_(Bucket=s3_bucket, Key=_key)
        if not verify_signature and not is_aws_cloud():
            assert head_["Metadata"]["wrong"] == "wrong"
        else:
            assert "wrong" not in head_["Metadata"]
    @markers.aws.validated
    def test_get__ignores_request_body(self, s3_bucket, aws_client):