openapi2kong does not generate configs for openapi specs containing external references

I believe the `deck file openapi2kong --inso-compatible` command has been introduced as the replacement of `inso generate` command.

But, unlike inso, deck does not generate configs for openapi specs containing external references.

Hence, we have to rely on separate tools like **openapi-generator-cli** to create a new openapi spec with all the external references bundled in it.

Please fix this issue.

Start with the `deck file openapi2kong --inso-compatible` command and compare its handling of external references with the `inso generate` behavior described in the issue. Reproduce the case using an OpenAPI spec with external references; done means the command generates Kong configs without requiring `openapi-generator-cli` to bundle the specification first.

Written by the indexing model from the issue text.