This allows importing the generated .pb.go files into other go projects.
I initially looked at buildGo.protos, but it doesn't work for multi-.proto
files, and actually having LSP support for the generated structs is nice, too.
Change-Id: Idbd448008010790a10a0ea42e4059dbb609eaf1a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7322
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>