### 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_
response = client.create_bucket(Bucket=bucket_1)
            snapshot.match("create_bucket", response)
            response = aws_client.s3.create_bucket(
                Bucket=bucket_2,
                CreateBucketConfiguration={
                    "LocationConstraint": secondary_region_name,
                },
            )
            snapshot.match("create_bucket_location_constraint", response)
            response = client.head_bucket(Bucket=bucket_1)
            snapshot.match("head_bucket", response)
            snapshot.match(
                "head_bucket_filtered_header",
                _filter_header(response["ResponseMetadata"]["HTTPHeaders"]),
            )
            response = aws_client.s3.head_bucket(Bucket=bucket_2)
            snapshot.match("head_bucket_2", response)
            snapshot.match(
                "head_bucket_2_filtered_header",
                _filter_header(response["ResponseMetadata"]["HTTPHeaders"]),
            )
            with pytest.raises(ClientError) as e:
                aws_client.s3.head_bucket(Bucket=f"does-not-exist-{long_uid()}")
            snapshot.match("head_bucket_not_exist", e.value.response)
        finally:
            client.delete_bucket(Bucket=bucket_1)
            aws_client.s3.delete_bucket(Bucket=bucket_2)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify
    def test_bucket_name_with_dots(self, s3_create_bucket, snapshot, aws_client):