Update OpenAPI spec and regenerate libs

[svix-jplatte]

This does the bare minimum to make CI green with the latest OpenAPI spec. In particular:

• This does not update any languages we don't have in regen_openapi.sh yet - we're going to add the remaining languages over the coming week or two
• This does not expose the ingest endpoint API in JS and Python - we want to generate an ingest resource API that has an accessor for an endpoint sub-resource, but the templates don't support it yet (this is also coming soon); for Rust I wrote this by hand to get rid of some "unused pub" warnings

[svix-mman]

@svix-jplatte I want to merge and release this today so the headers field on EndpointIn is released (For a JS customer)
Since we don't expose ingest yet, there should not be a problem committing the new struct enum logic without testing it first right?

[svix-jplatte]

This version of the spec doesn't contain any struct enums yet anyways.