[Fabric] replicate spec version syncing from fabric-go

[ctreatma]

The fabric-go GitHub Actions workflows were updated to allow the sync workflow to automatically discover the latest version of the Fabric v4 OpenAPI spec, download that version, and then regenerate code from the new spec. This reduces manual effort to keep the SDK aligned with API changes.

This is the PR that updated the fabric-go automation to pull in the latest Fabric v4 spec instead of requiring a manual PR to bump the spec version number: equinix-labs/fabric-go#30

It would be nice to replicate that work here so that we can avoid reintroducing the requirement for a manual spec version bump and so that we can build some momentum around using the Swagger API registry URL to discover new Equinix service versions (and possibly enable discovery of the services themselves).