Serialize with initial indentation - SimonSapin, pull/848
This helps use indentation in something that is partly but not entirely GraphQL syntax,
such as the debugging representation of an Apollo Router query plan.
Example: document.serialize().initial_indent_level(2).to_string()
Add validation requiring composite types declare fields - tinnou, pull/847
Object types, interfaces, enums, unions, and input objects must all have at least one
member. This is now checked in schema validation.
For after https://github.com/apollographql/apollo-rs/pull/849
Features
document.serialize().initial_indent_level(2).to_string()