C# proto include dirs

[UnstoppableMango]

Include dirs are kinda jank atm with having google apis as a submodule. Find some way to make it less jank. Could certainly be just symlinking the files we care about, but I want to at least look into it a little more before doing such jank.

Also at the time of creating this issue, it's only the C# that has jank imports, but I might have added more since then that need de-janking

[UnstoppableMango]

Went through a couple iterations since this was created. Tried Buf. Tried dotnet-grpc and gitignored the vendor files. Tried dotnet-grpc and checked in the vendor files. Now I don't think I even need manual intervention due to https://www.github.com/dotnet/aspnetcore/issues/43376.

Still would like to use Buf, but it's hard to get a workflow that works well locally and in CI.