Allow namespaces and routes to be renamed using the versioning library

[j-waters]

None of the versioning decorators work with namespaces, and there's no way of adjusting explicitly named routes without creating new types. Maybe we've been doing stuff wrong, but this meant that doing a recent API version bump was less smooth than I would have liked.

A simplified example - we started with:

@versioned(Versions)
namespace Service;

@route("/things")
namespace Service.Things;

model Item {
   ...
}

op list: []Item;

...more operations

We wanted to rename "things" to "stuff". I ended up having to:

• Rename the namespace to Stuff, which renamed a bunch of the generated openapi components
• Create a new interface, and move the route and the operations into it
• Mark the interface as "removed" in v2
• Create a second interface that extends the first, and mark it as "added" in v2

My issues:

• Renaming the Things namespace to Stuff caused a bunch of generated openapi components in the v1 spec to be renamed. Not the end of the world, but some people might consider that a breaking change. We could have duplicated the namespace and renamed the copy, but that doesn't feel ideal
• Changing the route required a new interface that just extends the first one. I'd much prefer to just have the one interface be able to change the route depending on the version

That being said, the experience is still miles better than working with raw openapi