allow specifying open api servers when constructing swagger docs

[ShahOdin]

👋🏽

open api allows specifying "servers" in a spec so that the user can toggle between them when trying to hit the apis. They allow both absolute and relative urls.

My own use case is the relative url. more specifically, this: smithy-lang/smithy#2233

Be nice to add them. Guessing it's not a priorirty in which case, please point out where in the code this could/should be done.