Include OPENAPI_VERSION into npm bundle

[arthurfiorette]

Why?

Currently, there's no way to trace back the openapi version to the generated client, since only VERSION is included, but not OPENAPI_VERSION.

When downloading the spec via https://raw.githubusercontent.com/stripe/openapi/refs/tags/<OPENAPI_VERSION>/openapi/spec3.json, OPENAPI_VERSION is required since versioning is not done using any other version value like 2024-12-18.acacia.

Having the file there would easily allow for a file read and access the right used version at runtime :)

What?

This PR simply as OPENAPI_VERSION into npm package contents.

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