Inconsistent package name of "transport"

[ryan-ju]

https://github.com/aws/smithy-go/blob/main/endpoints/endpoint.go

The directory is endpoint but the package is transport. This violates Go's naming conventions.

[lucix-aws]

I noticed this recently. I'm not sure what we can do about it without incurring a compiler break. We'll probably just have to spawn a new package and mark all the APIs here as deprecated, but that's a non-trivial lift to getting usage of this migrated over in generated SDKs.

[lucix-aws]

In fact, I don't even think we can address that, because it's going to break the signature of APIs generated in said clients (EndpointResolverV2 is typed to return this).

Leaving open for the record, but I don't see a future where this is addressed, at least in the downstream Go SDK.