federation v2 support

[dariuszkuc]

# re-generate schema
dotnet run --project compatibility/Products.csproj schema export --output products.graphql

# run compatibility results
npx fedtest docker --compose compatibility/docker-compose.yaml --schema compatibility/products.graphql --debug

Results

*************
Federation v1 compatibility
*************
_service PASS
@key (single) PASS
@key (multi) PASS
@key (composite) WARNING
repeatable @key PASS
@requires PASS
@provides PASS
federated tracing WARNING

*************
Federation v2 compatibility
*************
@link PASS
@shareable PASS
@tag PASS
@override PASS
@inaccessible PASS
@composeDirective WARNING
@interfaceObject PASS

TLDR need to think to think about how to support @composeDirective.