Investigate import issue with grpc-ecosystem/gateway plugin

[mfridman]

Likely related to https://github.com/grpc-ecosystem/grpc-gateway/issues/3801

The Generated SDK code is generating wrong imports and https://github.com/grpc-ecosystem/grpc-gateway/issues/3801#issuecomment-2072703665 explains fairly well how to reproduce it. Based on that structure when the separate_package=true option is enabled it builds an incorrect import in `service1/v1/service/service1v1gateway, specifically

- "buf.build/gen/go/.../service2/v1/service2v1grpc"
+ "buf.build/gen/go/.../service1/v1/service1v1grpc"

I suspect it's using a filename instead of the full path, but that's just a hunch.

Debug notes:

✅ strategy: directory ❌ strategy: all